best ever fuel mileage 2009 6.4L

2009 F-450 6.4L 4.88 gears.
Empty. Never driven over 70 mph.
45 mph brought it up .2 mpg from its overall average of 9.3 mpg.



Loaded 4.5 mpg. The snowcat weighs 10,000 lbs. Not sure how much the trailer weighs.

I would have thought that it would do better.