Great truck, still getting used to the new front end grill( I liked 99-02 best) I previously owned a 2000 z71 sierra slt. Just bought 2004 SLT 2500 crew cab 4x4. They dont include under the hood courtesy light, they eliminated one of the cigarette lighter power input. the 2004 has 6l vortec which is a huge pig compared to 5.3 vortec in my old 2000. the new computer stuff is pretty cool. I am getting on average 10mpg on the 6 liter, I used to get 18- 19 on the 5.3 motor. The first thing to go will be the air cleaner swap with an Air aid or K&N type of element. dramatic horsepower and fuel economy increases should be expected.
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.