If this particular trailer's "dry weight" is truly 7000 lbs I'd find it difficult to believe it weighs in at just 7700 lbs fully loaded and ready to camp. Regardless, 9.5 mpg pulling a barn door weighing almost 4 tons at highway speeds with an F250 seems reasonable to me. I typically see low 12s but I'm towing a 19 footer weighing well under 5000 lbs with my 1/2 ton Silverado - same barn door but a heck of a lot less weight, so expecting a 3/4 ton to achieve the same while towing so much more is IMO unrealistic.