We tow our 5th Wheel at 65 to 68 Mph.
Our truck will stay in 6th Gear without a lot of downshifts at this speed and our fuel mileage is about 10.5 mpg.
For a combined Gross Weight of Truck & Trailer at about 24,000 lbs. I think we are pretty good.
If I speed up and run 70 - 75 our fuel mileage drops to 9 mpg.
Robert & Bale the "Traveling Dog"
2012 GMC 3500HD DRW