The gas/diesel debate has gone on since the internal combustion engine was designed.
Gas: cheaper (slightly) to maintain, more stops for fuel, less torque overall.
Diesel: Higher torque, (possible) higher maintenance, longer life, retains value.
If 7796 is your GVWR, a 2500 gas engine will do just fine.
You are going to have to think hard though about future wants and needs. If you think you'll ever go larger, (and most of us have), you may want to consider getting the tow vehicle out of the way now. Moving from a 2500 to a 3500 (or 250 to 350 for Ford nuts) is not much more spaced out over a trucks lifespan. And, if you are ever going bigger, moving to a dual wheel 3500 now can pay off in the long run.
In my experience, (not much, 27 years of towing and camping now) I've had a 1500 to tow our popup (great!) and moved to a 28 foot (OK). Moving to the 30, the 1500 didn't cut it at all, but a F250 was OK with the 5.4 Triton, except on grades. Then it screamed in low gears, and lost speed quickly. "Torque is what I need!" says me, and I jump in the diesel pool.
Towed that 30 with an F250 with ease.
Traded for a 33 Jayco, 9200 pounds, upgraded to a larger diesel in a 2016 F250 . Zero problems, I could drag the moon right next to the earth if I could get it hooked up.
Currently have a 21 F350 Dually to tow the new 40 foot 5'er at 18k, and again, I'm not hesitant to go anywhere. 475 HP, 1050 foot pounds of torque. Aluminum body, (no rust) and heavy duty options (springs, axle, etc).
You'll find similar specs in RAM and Chevy, with GM trailing the pack slightly on torque and HP specs. No matter, they do just fine, frankly the Powerstroke and Cummins are just overkill unless you are at towing capacity limits.
If you have maintenance done, the diesel will cost more. Oil changes are gallons, not quarts, diesel has a tendency to be bit more because of the trucking industry. DEF (dieseI exhaust fluid) will add about 20 dollars every 4000 miles. Diesel fuel adds to combat water and keep things clean add a couple dollars to every fillup. Brakes are more stout as you go up in class, but cost more to replace.
I get right at 13MPG towing the 18K, a gas engine would be killing me at less than 9MPG. IMO, though, in light of the awareness on environment, and switching to electric in many areas, diesel will continue to be available for trucking... there just is no substitute. Gas will slowly dwindle, and supply and demand says it will go no where but up in price.
Aeron 5'er is right on. Can't have too much truck, easy to have too much trailer.
Go drive a diesel, you'll be pleasantly surprised.