GMT900 Overland build anyone?

[mrpeterclark]

Hello all, I currently own a 2000 LX470 which has provided 218k trouble free miles and has taken me all over US and parts of Canada. Alas, I find myself needing a bit more utility and have had my eyes on an Avalanche/Escalade EXT. I love having low range, but from what I’ve heard and read, not withstanding the above from @mrpeterclark, the 6.2 and AWD seems to work for most situations, even more so with the G80 rear.

My girlfriend and I have a little part time business setting up bounce houses which requires towing about 3k-4k every weekend for about 7 months out of the year, a task our Tundra is up to, but definitely not the LX with 33’s. Great vehicle but is a turd. Additionally, we are both considering getting motorcycles to ride together, and loading in the bed seems more convenient than getting a trailer. This would also be a vehicle that I would like to travel with just as much as the LX and still have a good degree of power, comfort, and most importantly reliability. Given this criteria, I would love one of the 07-09 Avalanaches with the 6.0 and 14bolt SF, but wouldn’t know where to begin to filter a search for one.

This leads me to my questions. I am no stranger to GM as I had a 94 Suburban 2500 that was a champ.

• Given that I will likely be towing several times a month, I’ve ruled out 07-09 and have elected to look for 09+ for the 6L80E. Will this transmission and the 5.3 be enough to handle this load in the hills of Western NC on a regular basis, and is there a gear ratio That I should look out for vs another - does it matter with a load like this?
• I don’t run hard trails, and think the motorcycle might get more seat time for harder trails, is there an ability to add a 2 speed transfer case to the 6.2, or would it be easier to just drop in a bigger motor into an Avalanche?
• Another angle I’ve considered is to keep the LX and get a cheaper GMT800, does this seem viable, or would I regret it when it comes time to attach a hitch?
• I don’t plan on lifting much more than perhaps a leveling kit and more aggressive tires, what kind of mileage do you see with the 5.3 vs the 6.2? (I haven’t ruled out the 8.1 2500 either, but know that the mileage is measured in tears now).

I think the 6L80 was available in the LTZ with the 6.0L - that would give you most of what you're looking for in the 2500 with a more comfortable ride minus the beefier 6L90 transmission. You should be able to filter by the trim level. Might be pretty tough to find. I'm Not sure if it came with a 2 speed transfer case or not. If it's selectable 4wd then the 1 to 2 speed tcase swap is not bad. Check the tahoeyukonforum out. There is good info there.
The Cadillac version of the avalanche has the 6.2 w/ AWD and a 6L80 same as my Denali. I know of a couple of guys that have done manual transfer case swaps into a Denali, but haven't found anyone that did selectable electronic shifting transfer case swaps into one. I don't know if GM used the same wiring harness and just taped up the wires behind the dash or if it's a different harness. One of these days I'll probably drop the cash and dive into it. If it's a paint I would probably opt for one with 2 speed tcase and 5.3 and swap in a 6.2 when the time came. I hope it's easy. I think compared to the LX a 5.3 will be great. If you use 4low frequently I think you'll find you wish you had it more than the 40 or 50 extra hp The 6.2 is a Camaro engine with a taller intake for a little better low end torque, but it's still a high revving engine which isn't necessarily great for towing. It is pretty fun though. The 6.0 is probably better suited for frequent towing and hills. I think the Avalanche is pretty cool, but also not a lot of support out there for bed racks and things like a pickup. It will require custom fab stuff. The Cadillac will be even worse in that regard, but if you figure out the transfer case swap let me konw. The Avalanche is pretty much the same exact thing as a suburban with the back configured differently. I would love to make a roof rack for one. Hit me up if you get one. We also got a bumper developed for the Avalanche and Suburban at baselineoverland.com

I get about 13-14 with my high mileage/ loaded down truck. I get 11-12 towing our off road trailer (at Colorado altitudes)

 

[Rosco862003]

I think the 6L80 was available in the LTZ with the 6.0L - that would give you most of what you're looking for in the 2500 with a more comfortable ride minus the beefier 6L90 transmission. You should be able to filter by the trim level. Might be pretty tough to find. I'm Not sure if it came with a 2 speed transfer case or not. If it's selectable 4wd then the 1 to 2 speed tcase swap is not bad. Check the tahoeyukonforum out. There is good info there.
The Cadillac version of the avalanche has the 6.2 w/ AWD and a 6L80 same as my Denali. I know of a couple of guys that have done manual transfer case swaps into a Denali, but haven't found anyone that did selectable electronic shifting transfer case swaps into one. I don't know if GM used the same wiring harness and just taped up the wires behind the dash or if it's a different harness. One of these days I'll probably drop the cash and dive into it. If it's a paint I would probably opt for one with 2 speed tcase and 5.3 and swap in a 6.2 when the time came. I hope it's easy. I think compared to the LX a 5.3 will be great. If you use 4low frequently I think you'll find you wish you had it more than the 40 or 50 extra hp The 6.2 is a Camaro engine with a taller intake for a little better low end torque, but it's still a high revving engine which isn't necessarily great for towing. It is pretty fun though. The 6.0 is probably better suited for frequent towing and hills. I think the Avalanche is pretty cool, but also not a lot of support out there for bed racks and things like a pickup. It will require custom fab stuff. The Cadillac will be even worse in that regard, but if you figure out the transfer case swap let me konw. The Avalanche is pretty much the same exact thing as a suburban with the back configured differently. I would love to make a roof rack for one. Hit me up if you get one. We also got a bumper developed for the Avalanche and Suburban at baselineoverland.com

I get about 13-14 with my high mileage/ loaded down truck. I get 11-12 towing our off road trailer (at Colorado altitudes)

View attachment 728031

Very impressive products you’ve assembled and has definitely put another tally in the Avalanche box. I’ll be going to test drive one today and would love to be the guinea pig for a roof rack, plus gives me a reason to visit CO again. Thank you for the clarification and information.

 

[Martinjmpr]

One thing I forgot to mention is that while all of the GMT800 4x4 Tahoes and 1500 Suburbans came with 2 speed transfer cases, starting with the GMT900 platform the standard T-case was a single speed on the Tahoe, Non-Denali Yukon and 1500 Suburban.

The Escalade and Denali, of course, have a full-time 4wd system (I wouldn't call it AWD although GM did) with a single-speed T-case and no controls of any kind for the T-case.

You can tell which one it has by looking at the T-case control to the left of the steering wheel. The standard T-case control will have 3 positions: 2hi, 4Auto and 4 hi:



The ones with the 2 speed T-case have a 4 low position as well:



AFAIK the 1 speed was the "standard" on the base model (LS) Tahoe and Suburban, not sure about the LT and of course the Z71 model or LTZ would have gotten the 2 speed case. Also, I have heard that if you ordered the "trailer towing package" it also came with the 2 speed case.

Keep in mind this only applies to Tahoes and 1500 Suburbans. Avalanche models (last year for the Avalanche was 2012 I believe), pickups and 2500 Suburbans all came with the 2 speed case.

 

[Bob Boyer]

Hey, it's not a rock crawler, but if you want to travel and travel off-road to most of the places a big vehicle will fit, the GMT900 is seriously capable with just a few mods. I bought my 2011 Suburban with 231k on the odometer, I just got back from our second lengthy trip this year with 262k on it and the 5.3 hasn't laid down yet while pulling a 17' Winnebago TT through some serious hills and mountains. We never drive less than 2500 miles pulling the trailer and have made multiple trips since I bought it in 2020, including 5500 miles through Arkansas to get to Big Bend, Fort Davis, Carlsbad, and Palo Duro Canyon and back. That said, the first thing I did was install a DiabloSport dongle on the ODBII port that overrides the AFM and keeps all 8 cylinders running full time without having to use the Tow Mode. It's not an optimal solution but a remanufactured 5.3 without the AFM/DOD is in my plans if and when this one finally says "no more". And I'm truly anal about oil change intervals. 5K max with full synthetic, or as soon as I get back from a trip. Driveline components and transmission will get fluids changed at 50k intervals. So far, so good.

I bought it with a leaking radiator so it got a Cold Case 3" thick aluminum radiator with a Tru-Cool transmission cooler in front of that. Temps stay where they're supposed to, even in this heat we had last week over here in the southeast. Underneath, I ripped out the air-ride suspension bits and replaced with Z71-spec Moog rear springs, Bilstein 5100s, and air bags for towing. The rear springs and Bilsteins lifted everything about 2" without any kit needed. The wife thinks the ARB compressor located on the second battery shelf up front is the best mod ever. 275/65-18s General AT-Xs on Silverado take-offs work well in the slippery stuff, with and without 4WD.

This rig pulls our trailer very nicely. If I keep it, I'm contemplating 3.73 gears - the 3.42's in it aren't quite what I'd like but 4.10s will just rip a gas budget to shreds right now. If and when I do that, it will get a replacement for the G80 limited-slip. I've also taken notice of Mr. Clark's offerings at Baseline Overland as it looks like he's solved some issues very nicely. And if you want to see a really well-built example of a Tahoe, ImNoSaint's build thread takes one to a whole other level: https://expeditionportal.com/forum/threads/imnosaints-tahoe-build.222750/

I'm definitely in the camp that thinks these and GMT800s are undervalued vehicles for overlanding anywhere in the Americas.

 

[ThundahBeagle]

@socal4n4 There are a few on here with the GMT900, myself included. Really depending on what you want to do with it, the GMT900 is awesome, but the GMT800 is also a great candidate and can also be had for a good price. If you are really looking to rough it up, take it on some pretty hardcore trails and it will see more dirt/two lane highway than say interstate driving, the GMT800 may be a better bet. These have more aftermarket support from what I have seen, especially in the way of armor (bumpers, etc.). Plus there are some pretty sweet builds on here on the GMT800 platform. Look for threads by @CrazyDrei and @02TahoeMD and @dirtdobberoffroad. These guys have some awesome builds. Also, if you want to find one in good condition, has gone through a full maintenance check, has mild suspension and tire upgrades, AND already has the inside built out from anything with just a drawer system in the back to already having a full sleeping platform build in the back - check out Suboverland.com. I almost went this route when buying mine suburban. HOWEVER...

I wanted to be different. I never saw many GMT900 builds (at least not suburban, on instagram you can find a handful of Tahoe builds that guys have built for desert offroading with long arm kits and stuff), so I got a 2007 Suburban. I think one of the great things about these is you get all kinds of tech and creature comforts, still at a decent price. I have heated front and back seats, power everything, leather everything, all in great functioning condition. But I do have the LTZ package. Which depending on what you want to do with it, I would say avoid! Because the LTZ has the air-ride suspension and its a PITA when you replace it because of the sensors. If you are not going to change suspension and this is more of a family long distance cruiser and campground rig, you could leave it. The ride quality is amazing. But I wanted a lift and bigger tires so I replaced mine with a leveling kit, new shocks all around, and HD springs in the back and stuffed 33.5 (almost 34") tires under it. Still rides great and cruises on the highway at 75 no problem, but I have dash lights and "warning" messages to check suspension components all the time haha. Again, aftermarket support is hit or miss, mostly misses. There is some crossover with the silverado of the same gen for front suspension components but most other stuff will then involves some level of custom work. Unlike Toyota's which you can buy anything for and Lexus seems to be getting lots of attention too in the aftermarket lately, you may need to get a bit more creative.

Here is my build thread and a pic of how mine sits right now: https://expeditionportal.com/forum/threads/2007-suburban-mudhorn.208787/
View attachment 644035

Nice one

 

[mrpeterclark]

Very impressive products you’ve assembled and has definitely put another tally in the Avalanche box. I’ll be going to test drive one today and would love to be the guinea pig for a roof rack, plus gives me a reason to visit CO again. Thank you for the clarification and information.

I just got an Avalanche all lined up locally. We will be prototyping and installing the roof rack soon. Let me know when you're ready for one!

 

[Norco_overland]

I just got an Avalanche all lined up locally. We will be prototyping and installing the roof rack soon. Let me know when you're ready for one!

Can’t wait to get that bad boy on my Av!

 

[ejwebb]

 

[ejwebb]

Tahoes work just fine, they are not rock crawlers. Hauls all the gear to Mexico

 

[ThundahBeagle]

View attachment 730671

That's an 800, though. I hated them when they first came out but they grew on me

 

[mrpeterclark]

Very impressive products you’ve assembled and has definitely put another tally in the Avalanche box. I’ll be going to test drive one today and would love to be the guinea pig for a roof rack, plus gives me a reason to visit CO again. Thank you for the clarification and information.

got the Avalanche Roof Rack up on the website recently and have a few photos from Norco_overland
Love his rig.
baselineoverland.com

 

[mrpeterclark]

A couple recent photos from our last mountain bike race in Eagle, CO

 

[ejwebb]

 

[ejwebb]

Here is from 10/12/22 in Mexico 50 miles north of Rocky Point. We had a 4.0 earthquake one night and a huge storm before that making it one trip to remember.

 

[phsycle]

Anyone else building GMT900’s?

I’m potentially looking at a 2013 Tahoe for ski trips and glamping mobile. Very keen on one that’s for sale—nice color and Z71 package.
Only mods it’ll get are small lift, 33’s, full length roof rack, and a dongle to deactivate AFM.