Congrats. I have just under 30k miles on my 01' Duramax Crew cab short box. I love it.
It gets twice the mileage of my 99' 454 and has twice the power! There are some pretty good hills on the way to the lake it doesnt even down shift out of overdrive my old truck would drop to 3rd gear. The allison trans is great too. I really like the way it down shifts in the tow/haul mode it saves the brakes. Good Luck.