01-04 (LB7) are bad on injectors. 04.5-06 (LLY or LiLlY) were sporadic with the injectors. 06-08 (LBZ) seem to be decent. 08-present (LMM)....couldn't tell you. Newer one's are even better, I presume. Front wheel bearings are notorious for failure on 01-07 models. Search THOROUGHLY for any evidence of a programmer.
The Allison automatic in the 01-07 trucks are identical INTERNALLY, only the 06-07 models with the six speed use a 32 bit controller as opposed to the 16 bit controller found on the previous models. They are not interchangeable. Fun fact: Although GM increased engine output over the years, the transmission design didn't change to reflect that. With the 01-04 model, 90 HP over stock was about the max with a stock transmission. As the model years progressed, that buffer decreased. The 06+ models pretty much had to have an upgrade to survive any HP increases with any kind of longevity.
Manual transmissions were good, but I think there was an issue with the dual mass flywheels (DMF) and HP increases.
Other than that, expect GM's typical mediocre interiors and torsion bar front suspension. Also, if you get a dually, be careful with the bedsides. They are $$$ if you break one. Ask me how I know...LOL!
