The loaded trailer would be in the neighborhood of 6,000 pounds, less than a third of the F-350's stated towing capacity. Running empty to pick up the trailer, fuel mileage hovered around the 16.5 mpg range. Surprisingly, the mileage dropped to 12 mpg when towing the empty trailer at around 2,000 pounds, then only dropped a half an mpg or so more with another 4,000 pounds of the barn find loaded up. Wind resistance may have more of an effect than weight on fuel mileage when towing. Along with ultralow sulphur diesel fuel, diesel exhaust fluid must be added for emissions control. Ford says the Super Duty has the largest DEF tank in the competitive set, and in over 1,200 miles that needle did not come off of full. Average over a week was 13.0 mpg. The balance when not towing was a mix of highway driving; this barge was not first pick for piloting around town.