My first gas tow vehicle was a 2003 Ram 2500 with a 5.7 Hemi gas engine. It did a good job with our 25 foot TT, but when we went to a 29 foot fifth wheel camper, the truck struggled and the transmission seemed to constantly shift and the engine would rev constantly on even on the slightest grade on the highway.
I switched to diesel and have never looked back. The oil changes for diesel have cost more money. But not enough to change my mind. I also have the fuel filter changed in the spring and fall. That will cost 100 bucks each. Other than that, not much difference. Towing with the diesel makes a big difference on grades. Pulling up the grades is easier and going down the grades is not a problem with the exhaust brake. That being said, if you have a smaller camper then a gas truck will do the job.
My 2500 Hemi averaged about 13 MPG with 4:10 gears. My 6.7 Cummins averages 14 with 4:10 gears. These are daily driving numbers.
