Up to 6000 miles and getting @ 8.9mpg towing 11,000lb 5th wheel on hwy. No better than 14 hwy., with no trailer, and 12 around town. Hoping 10,000 miles + helps, but not too confident! When I see another '08 w/trailer, always the same = fuel mileage 'suks'!! ----2008 F350 SRW 4wd