I have an 07 NNBS Sierra Denali AWD that I would like to up the horsepower on. But I had a couple questions... What are the limitations power wise for the AWD system, and also the trans? Is my trans the 6L80 or the 6L90? What would need to be upgraded for 600-650hp, with a few boosted launches possible(turbo build coming soon). Truck has 123k miles...

Also, when driving along at highway speeds, if I floorboard it the truck downshifts a couple times, hesitates for a half second, then clunks pretty decent before the power gets to the ground. I had my mechanic check it out and he found nothing wore out, such as U-joints, etc. So not sure what's going on there exactly.