My 06 GM 5.3 gets 11mpg with that weight at 8K ft now .
My 05 GM 5.3 only got 6.5-7 pulling 6000lbs. I got around 13-14 empty in the city.
If the Ecoboost gets 10-12mpg real world #'s pulling 10,000lbs, then there gonna sell a bunch of them. My Duramax barely gets that. How does it stop, or handle the swaying when the wind blows pulling that much weight?