Does your truck have the Allison tranny? I've been considering different tow rigs, just haven't decided on one yet. My dad has a suburban with the 8.1/Allison combo but he gets about 8 MPG while towing and 11 or 12 unloaded. No experience with the 6.0. Thats in flat Illinois, I'm sure it's worse in mountains or hills.
'00 TJ 3 spd, D30 aussie locker/8.8 E-Locker, Currie springs, Savvy/Currie arms