I have the 2500HD 6.6L Diesel 4x4 Crew Cab SB. This is my third GM 4x4 truck, but first diesel. I tow an RV and put dirt bikes in the back and it drives like I have nothing attached and nothing in the back. I can accelerate going up hills on the freeway fully loaded towing the RV. The interior noise is quieter than my wife's Chevy Blazer. The stereo absolutely rocks, and the seat heaters are so nice - even in San Diego CA! This is the best truck ever made.
Diesel engine, Allison transmission (in tow mode the thing starts down-shifting on the freeway from 5th through 2nd and sounds sooooo cool while helping slow you down, stereo, seat heaters, roomy crew cab, comfy seats and interior features.
This is the best truck ever made and there is nothing necessary to improve it.