This probbly isn't exactly the response that you were looking for but it may be interestomg to some. I have a 7.3 litre Excursion with 77,000 miles- all stock. About 3 weeks ago drove from Port Huron, MI to Cape Cod, MA, about 719 miles. I was pulling a Mercury Sable sedan with a front end dolly. The cruise control was set at 70 mph all the way and the outside air temp was in the lower 60's. Also had both the Sable and Excursion full of stuff from my mother's estate - maybe another 800 pounds. For the total trip I used 47.5 gals of diesel or 15.13 mpg (the overhead computer showed 16 mpg).