07 GMC Duramax/Allison 3500 Dually 4x4 L/B C/C got 16mpg on my trip out to Texas towing our open trailer and the same on the trip back with the Valiant loaded.....we got 14mpg towing Jimmy's 32' Enclosed loaded with his Dart when we took it up to Tony's to get wired up.....I got anywhere from 7-10mpg towing the 50' L/Q loaded. All trips are normally at 70mph interstate speeds.

It averages between 16-17mpg with no trailer on the interstate and 15mpg in mixed city driving...for the huge beast that it is, I'm very pleased.....

Rickster