Still researching - some GM specific questions: GMT 800 platform vs. 900?

[Martinjmpr]

OK, still doing research on my future full-sized-vehicle purchase, probably to happen next year...
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Wait, first off, before I start, are there any good message boards out there for full size domestic brand vehicles, specifically Ford and Chevy/GM? I've searched but have only found a couple of forums that were very 'buggy' (that is, lots of graphics running in the background that make it slow and difficult to navigate) as well as being rather 'dead' in terms of activity (maybe because they're difficult to navigate - Ya THINK?)
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That's why I come back here. But would still like to find a decent Chevy or Ford message board just to mine the "institutional knowledge" that is out there. Certainly I learned a lot about my 4runner from hanging out on the www.t4r.org message board.
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OK, back to my question: So I'm cruising the various ad sites and seeing what's out there and it seems to me that there are a few GM vehicles (Tahoe and Yukon) within my projected price and mileage range (under 125k miles and under $18k) that seem to straddle the GMT-800/GMT-900 divide. The 900 platform was introduced for the 2007 MY.
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I have a general rule that it's a bad idea to buy the first year of any "new" model so I'm very leery of the 2007 model. Which for me means I'd be looking at either a higher-mileage 2008+ or a lower mileage 2006-.
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My question for the group here, then, is this: Has anyone had experience with BOTH the GMT-800 (2000 - 2006) and the GMT-900 (2007-2014) platforms? And for those who have, how would you rate them?
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Looking through Edmunds I see that the 800 had a torsion bar suspension while the 900 has a double wishbone coil suspension. Presumably the 900 would be easier to do a mild lift on (which is the only kind I'd be interested in anyway.) The 900 also IMO looks better. I figure either one would be adequate to pull my trailer and do mild off roading as well as being my winter bad-weather/family hauler. The engine, transmission and 4wd systems seem to be the same (the 900 didn't get the 6 speed tranny until 2009 - is that something I should hold out for?)
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Were there any "known issues" with either platform? I read a little about cracked dashes in some of the '07 models.
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Thanks in advance for any replies or advice! :ylsmoke:

 

[4x4x4doors]

Been a while since I spent much time there but www.gmfullsize.com was once a pretty good source for GM info. Still seems to be moderately active although a lot more Ad-dy than before. Looks like they have sold out a networked auto forums group now though. I noticed one of their linked forums is http://www.tahoeyukonforum.com/ Just some thoughts.

 

[Mike1volfan]

I can't speak for the 900 but I love my 2000 model. No issues to date, I've got 94,000 miles on it now..The mild lift was relatively easy with new keys for the torsion bars, longer shocks and rear coil spacers. Still a work in progress though..

 

[justcuz]

Rear suspensions are the same for both models. Coil spacers or air bags are options. My 2000 Suburban has Autoride, so I did some research and found Hummer H2 springs fit. They are progressively wound like a Moog Cargo Coil and I have been real happy with that choice. They resulted in about 2" of lift.
GMT800 Avalanche, Suburban and Tahoe/Yukon front torsion bars are shorter than pickups. Either heavier Suburban bars or Ford pickup or Expedition torsion keys can be used to re-index the bars for 1-2" of front lift. I've never actually researched Ford torsion bars to see if they would swap in.
GMT900 have the front coil overs and I'm sure there are leveling springs or spacers commercially available.
The front fascia/bumper on them seems to have less clearance than previous models and not everyone will want to cut it like the border patrol does with their Tahoe's.

I just purchased a 2015 Suburban and I like the six speed trans. Driving it down from Palomar the downshift buttons on the shifter allowed me to choose between 2nd and 3rd to control vehicle speed very nicely. The shifting is also pretty seamless.

Another thing about the new Suburbans and Tahoes with V8 engines is they now come standard with the 9.5 14 bolt semi float rear axle. This is a much stronger rear end than the 10 bolt and will last the lifetime of the vehicle. These have the same 5 link rear coil suspension of the previous 2 generations, so once available in the wrecking yards will make a nice upgrade to any earlier model. Hummer H2's had electric lockers in these rear axles and there are multiple other traction devices available.
Some simple upgrades can be made to the 4L60E trans, (easily researched) and of course a good transmission cooler.
I would recommend 3.73 gearing, I don't know if they ever put 4.10's in Tahoes, but 3.42 gears are not enough gear for larger tires. I run 285/75x16 tires on my 1993 and 2000 Suburbans (32") and even though I would prefer 4.10 gears, the 3.73's work just fine.

 

[Somecallmetimm]

I drive an '05 and love it. 125k on the clock and it's running strong. Additionally I have a 2003 in the fleet I manage that's got over 250k, and other than maintenance, the only work done on it was to have the t-case replaced due to lack of use.

The GMT800 is a great platform with a strong and reliable drive train.

 

[Martinjmpr]

I would recommend 3.73 gearing, I don't know if they ever put 4.10's in Tahoes, but 2.43 gears are not enough gear for larger tires. I run 285/75x16 tires on my 1993 and 2000 Suburbans (32") and even though I would prefer 4.10 gears, the 3.73's work just fine.

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Is the gearing information on the sticker on the door? If not, how can I find out? Would I have to run the VIN to know the axle ratio?

 

[02TahoeMD]

Hi Martin. Couple of good reference sites would be z71tahoe-suburban.com and gmc4x4.com, both are practically ad- free and contain a good amount of information, though z71 has been around longer and thus has more stuff to search through. Another forum I visit that is not too bogged down with ads ( has some ) is tahoeyukonforum.com. Agreed that some of the other GM-centric forums can be a drag to deal with and I rarely visit them unless I am searching out information for a project. It seems that politeness is often hard to come by so I usually only "pass through" many sites just to get info and not participate in a conversation that may raise my blood pressure. Makes me appreciate ExpoPortal all the more.

I own a GMT 800 and love it, my work truck is a GMT 900 Tahoe and I am kinda...."meh" about it. The build quality of the 800 seems to be better in my opinion. Lotsa plastic (ok...tons) on the 900 platform compared to the 800 series SUV which thankfully still had real bumpers front and rear. That said, I still prefer my 2011 Tahoe work truck to the 2005 Expedition I used to have.

 

[justcuz]

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Is the gearing information on the sticker on the door? If not, how can I find out? Would I have to run the VIN to know the axle ratio?

It's in the bottom of the glove box. All the option codes are there. GT4 is 3.73 and G80 is the Gov Lock.
Most GM option codes can be found by googling "GM RPO Codes" cars and light trucks have some differences but not many, but you can refine it by inserting the make model and year of vehicle in your search.

 

[justcuz]

Since your current vehicle is a 2007 Toyota 4 Runner, have you given any thought to a first generation Sequioa?
Anything Tundra would work for the front suspension and rear springs could be found or wound by any competent spring manufacturer.
It is similar in size to a Tahoe, is my main reason for mentioning it.
I would never suggest an IFS Land Cruiser, because they are too expensive and cheaper vehicles can be built to equal one for a lot less money.

 

[Martinjmpr]

Since your current vehicle is a 2007 Toyota 4 Runner, have you given any thought to a first generation Sequioa?

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Yes, the 1g Sequoia is a contender but honestly if you look at the numbers it doesn't really stack up to either the GM or Ford. Prices are also higher due to the "Toyota tax" which I'm getting tired of paying.

 

[justcuz]

True, true. There is a real reason that the Tahoe was the best selling SUV for several years. Your "Toyota Tax" comment is right on.

 

[chaos616]

There may be a few folks out there that have experienced both but unless someone is always buying new trucks, most people will have extensive experience with 1 or the other. I don't buy new trucks so I only have experience with the GMT-800 Heavy Duty Trucks and Light Duty Trucks. That being said, the GMT-800 is getting old now.

Light Duty GMT-800
1999 Chevy Silverado/GMC Sierra hybrid ext. cab short box 4.8L 4L60E (Co-worker, i've wrenched and driven truck)
2001 GMC Sierra ext. cab short box 5.3L 4L60E (Fathers, work truck, my truck)

Performance, there were a whole host of engines offered in different levels of truck, however the 4.8L and 5.3L were fairly common as I understand it. the 4.8L is not a powerhouse, good enough to move the truck but suffers mileage at higher speed driving (70+) and isn't going to be towing very heavy trailers without either mechanical issues or at least complaining a lot. The 5.3L is a bit better for power (considering one for a blazer prerunner build currently) and would certainly do better for towing and high speed mileage, however it still isn't a torque monster and is still going to complain a little pulling dual axle trailers.

Reliability, I think the platform is fairly reliable in my experience, very few issues with mechanical failures, even the IFS is pretty tough if used in an appropriate fashion. the 4L60E transmission is pretty good, although only a 4 speed, does tend to be tall on the gearing in the sense that a 5 speed could have been nice once in a while. The 5.3L i had did start having some issues with smooth idle, however at 150,000 miles and the lack of maintenance performed on it before I got the truck probably didn't help. It ran great otherwise and pulled pretty hard.

Frame/drivetrain, it is light duty on these trucks, payload is lighter as is the vehicle itself. Makes them almost more fun to drive than the HD version of these trucks. Running gear is a little light, but plenty tough for the nature of the vehicle itself. Mine had the autotrac NP246? t-case, no issues except GM wants an arm and a leg for the Autotrac II fluid. Transfer case worked well as advertised, only issue was it would kick in real hard if you had it in auto 4x4 and spun the back wheels too much, if you wanted to engage in hooliganism then just put in in either 2 or full 4. I've heard the 8.25" IFS on the front is weak, i've never had issues and used the truck a lot in rough situations, i think for the weight of the vehicle its fine. The rear axles are Semi-Float but still hold up well, also its reported the G80 is weak, i've not broken one yet.

Overall, i have had a good impression of these trucks and would buy again. Also I never ran oversize tires or any real modifications on the Light Duty GMT-800. my 5.3L finally died as result of 70 mph + Cow.

GMT-900
2007 GMC Sierra ext. cab short box 6.0L 4L80E (Mine, bought 90,000 miles now 157,000 miles)
2007 GMC Sierra crew cab short box 6.6L Duramax Allison 6 speed (Fathers bought new now 170,000 miles).

Performance, I don't have any experience with the 8.1L although I have heard from others its a beast for pulling, but your wallet will cringe. The 6.0L i run is a fantastic motor, very tuneable if you have the software. The 6.0L has plenty of power stock, with oversize tires you'll be wishing for a little more. Mileage sucks but is very very consistent. I get around 12 mpg both in town and on highway, offroad is worse i'm sure. When i got the vehicle stock with 90,000 miles it only got 13.5 on the way home. Even after modifications it still holds at 12 mpg. The 6.6 duramax is, as to be expected, a mountain of torque, it will literally pull a house. The 6.6L i have experience with gets around 21mpg (at 160,000 miles) highway empty and with a trailer about 16-18 mpg (trailer weight of about 5000 lbs. dual axle). The Allison is an awesome transmission with the diesel and works very well. The truck runs and idles smooth, and cold starts really are no problem with the 6.6L (cold starts as in -40 F, truck lives in northern MN).

Reliability, The 6.0 L thus far has been really reliable even at higher milage, maintenance has always been fairly meticulous as far as oil etc... Only real issues of the 6.0L yet that has had to be changed or delt with was the AC belt tensioner pully (in an exposed location for offroad use). The 4L80E was a good transmission, although because of modification was switched for a more maintenance free/simpler transmission. I have changed almost everything on the 6.0L except the motor and it is still stock with a blackbear tune (mostly tuned at this point for switched components related to the engine, like transmission, t-case etc...) the 6.6L is really quite reliable as well, a couple of power steering hoses had to be changed but I have a feeling that was due to the temperature extremes in northern Minnesota (100 F summer up to 100% humidity, -50 F winter with down to 5% humidity). The Allison transmission has also been maintenance free.

Drivetrain, the best part of the HD trucks, everything is really quite beefy, even the IFS is now a 9.25" ring gear and quite tough. All of the IFS arms etc... are much tougher in the HD truck than the LD trucks, they are a different design and can take some abouse. That being said, its not a straight axle as far as pure beefyness. in the 6.0L the original 4L80E was a beefy transmission, but due to electronic issues, has been swapped for a NV4500, even beefier. easy swap due to LS based engine design and bellhousing patter. Some of the trucks came with NV4500 to start with and some came with the ZF 6 speed (only diesel and 8.1L). The 14 bolt rear end is something of a legend in the offroad world, because its cheaper than dirt and tougher than nails. 10.5" ring gear is great (I run two of them on the truck now). That being said, i have bent my 14 bolt on the 6.0L truck. The only difference besides transmission and engine in the 6.6L is the rear end is also a 14 bolt i believe but a different axle housing as it has an 11.5" ring gear. So far no issues.

Overall, i have been pleased with the durability of the HD GMT-800 platform, I have never been left walking by any GM truck of this class. The only downside so far has been the sheer weight of these trucks compared to the LD trucks, they are heavy and my current 6.0L is around 8500 lbs.

I have absolutely no experience with the GMT-900, we considered buying one, however my only reserve was the amount of electronics (there's even too many on the GMT-800) and my significant other thought they didn't look as cool as the 800 (very scientific).

Ok, i'm done.

 

[Martinjmpr]

True, true. There is a real reason that the Tahoe was the best selling SUV for several years. Your "Toyota Tax" comment is right on.

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What's funny about the Tahoe is that for some reason I had always thought of it as an enormous vehicle, being "full sized" and based on the Chevy full sized pickup platform.
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Then I was camping last month and one of the other people there had an older Tahoe (a GMT400 version) and he parked right next to me and I realized his Tahoe was only slightly longer and wider than my 4runner.
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I like the size and the "look" of the Tahoe but the more I think about it I think the extra fuel capacity of the Avalanche or Suburban is going to tip the scales for me (31 gallons in the Suburban/Avalanche vs. 26 for the Tahoe.)

 

[justcuz]

I own 4 Suburbans so you won't get any argument from me!

 

[rayra]

My '85 C-10 standard cab long bed pickup and my '02 Suburban are within about an inch of each other in overall length. Practically the same wheelbase too. Been no changes required in driving habits. Our Tahoe thanks to its shorter wheelbase has a seemingly much tighter turning radius than the Suburban. If you crawl around in tight mountain or forest roads, that might be an issue. The departure angle on the Sub is much worse than the Tahoe, which ain't that great either. But both have the heavy duty tow kit hanging down so that's sort of moot.