Mine is a 2005 Ford E350. I tow a 35ft. trailer weighing between 8700 and 9200 lbs. loaded. By the way, mine is a reworked, bullet proofed 6.0 diesel. I can travel at whatever speed I need, and that is normally 65mph, that's where it likes to run towing. I get 13mpg towing that size and weight. Oh, it also has a Livewire TS programmer and I tow with the 65 horsepower added towing mode. Mountains back in the east....W.V., Pennsylvania, etc. seem to be rough on anything, have more trouble back that direction than in Colorado for whatever reason.