i've got an 06 2500hd crew, 6.0/4.11. it's been a good truck for me so far. i'm right around 50k on it now, and while under warranty i had the intermediate steering shaft and a tie rod end replaced. sadly, soon after the warranty went out it developed a front main seal leak. it's very minor, and i haven't addressed it yet, though eventually i will have to. for now i am just monitoring it.
as far as towing goes, i've been content with it. i've owned enough 1/2 tons and no matter what they rate them at, i don't like them for towing anything past small recreational vehicles (snowmobiles/atv/small boat). i generally tow from small compact tractors to full size light duty trucks on my trailer, so usually 6,000-8,000lb combined. i once towed a ton dump on the trailer, so combined around 10,000lb and it was more weight behind me than i'd want to do on a regular basis with that truck and trailer setup.
for the motor's power i can't really complain considering the size and weight of the vehicle. i would consider the 6.0 a direct replacement for the 5.7 (350). it may look slightly better on paper, but from my driving experience it is pretty much the same. the 06 is virtually identical to the 00 2500 (classic) 5.7/4.11 i had previously, though i manage about 1.0mpg better economy with the 6.0 (i attribute a lot of that to the onboard dash gizmos that tell me how far i can go on a tank of fuel).
empty i can usually get right around 15mpg in the summer, but it has been my experience that in everyday driving you do best at 45-50mph. it will drop off a couple mpg at over 55mph. i drove it to florida once (pre-e10) and managed 15mpg round trip while doing a consistent 70+mph, but if you drive that fast and vary the speeds for local driving you're likely to get 10-12mpg.
