7.1 MPG isn't that bad. Go back 10 or 15 years when there was competition and check the mileage data. Owners would have jumped for joy to reach 7 MPG combined with the HP and torque we now have. Pushing 20,000 pound 11' x 9' X 30+' box that has air conditioners, satellite domes, awnings, jacks, tank dump valves and who knows what else sticking up, out and down and I'm pretty amazed I get the mileage I do. Throw 3000 pounds on the back end and I only lose maybe a 1/2 mile per gallon! Any other vehicle and the numbers would be half the normal average, if you're lucky.
For what we as owners/drivers are demanding of our power trains Ford and GM, when they were supplying, are producing a reliable, powerful, easy to maintain and affordable foundation for our rigs. What I can't image is how our fathers got us to Florida, California or what ever for summer vacation in a 1968 something or other we road in the back of with no AC, no DVD players, no XM radio,,,