Ive been towing with an 02 suburban with the 5.3. I get 13 towing staying at 65mph, but it does struggle when I go up hills. the storage is awesome, being locked and secure. I've looked at the 6.0 LQ4 engines, they have alot of power but I haven't heard anything good about the fuel economy of them. I know a guy with one and he gets 8-10 towing and 12-14 unloaded.
A tahoe with the duramax allison combo would be bad ass!!!