We are towing about 9200lbs with a '13 Chevy 2500 6.0. Granted, we are in Mi, but It does good. Have had the trans drop into 3rd when heading Up North just North of West Branch, Mi where there is a slow, continuous incline. 4th was just not enough to maintain speed (about 67mph), with speed dropping ever so slightly. Gave a little more gas, trans dropped into 3rd, and I could have accelerated to "X"mph if I wanted.
We have averaged about 8mpg towing if I recall. The typical 7-10mpg still applies for the gas 2500/3500. Even my Buddy's '13 Ram 2500 Cummins towing his 4 place inline snowmobile trailer only got about 12mpg (may have been 11mpg.. Can't recall for sure!) loaded with 4 sleds when we went on the guys trip this past Feb. And it was only 2 of us in the truck.
Any of the Big 3 2500/3500 Gassers will work. Only you can really decide if the diesel is worth the extra cost, regardless of buying new or used. For the right price, I would probably buy a diesel, but it would have to be one heck of a deal. BUT our needs may change down the road and maybe we would need a diesel. Though some of the newer gas trucks are rated for up to about 15k lbs I believe it is.
Good luck shopping!!!
