that will be a real cool conversion, i wish i had the duramax in my 2003 2500hd, they are a heck of an engine.
my friend's dad has an 2006 3500 4x4 duramax with allison, and that thing is unreal, we had a 35 foot enclosed gooseneck loaded down with atvs/fuel/camping stuff, and you just let in on the throttle and you can pass big rigs like they are standing still or may be 75
