The last gen with the 6.0L TD's were rockets but had issues with head studs and gaskets espesicaly when "tuned" with a plug and play computer deal. The 6-spd 7.3 combo would be great, those motors were alot better but not as much of a hotrod motor. I don't know much about the new navistar motor, but I've heard the first run had issues???
I drove an 05 for over a year working for my friend's landscape construction company. I liked driving it, good seating position, I like how you sit upright and your feet go down to the pedals. For long trips the quad cab was really nice and the thing rode really comfortable. They're long but honestly they're pretty easy to manuver. as was already said, when tyou hit the open road they really shine imo, the miles just go by alot easier with that big diesel and all that room/wheelbase. Compared to driving my 4Runner the same 500 miles, the SD was a dream on the highway, (yes I just dissed my toyota in a Frod thread, what has happened to me???

)and imo suprisingly quiet.
Watch out for the front D-50 in the, I belive, 250's of some years, it's kind of a dog and has very little aftermarket support from what I understand.
Unlike the awful manual trannys of the Ranger with what I call one of the worst clutches in existence, the SD's manual trannys are nice to drive. I like driving stick so I'm biased, but the same frind replaced that 05 with a new 08 and I really don't care for an auto in those big trucks. I like the control of a manual espescialy when you're driving that beast around town. We wheeled it quite a few times both in the snow and mud and the rocks and honestly, it did pretty good. It's really long, but it felt solid and never left us stuck plus we always came home with alot of firewood in that huge bed
another opinion of mine is that the new interior is just plain hideous... I liked the old plain janeish interior of the previous gen as well as the general exterior appearance. I'm not a fan of the giant tonka toy grill on the new ones.
Personaly, I'd rather have a Dodge with the Cummins in it, but Ford the Ford SD is my second favorite of the Domestic big-rigs.
I'm still kind of semi-hunting for an older F-350 crew cab, the boxy ones from the 90's for a rafting long-hauler. Here in the NW, they're everywhere and just blend right in leading to less of the wrong people wondering what's in the truck. I like the older body style too, pretty classis american iron to me, although I really liked the 05 I mentioned too. A simple leveling kit and some 35 old BFG MT's and it looked GREAT... it was white too so that didn't hurt.
that's my long-winded .02
Dave