Go with the diesel. Everyone has their own mpg stories. But my hauler is 5,200 dry, 7,500 with water, coolers, quads, etc. and I get 8-12 mpg depending on speed. At 60 mph I'll get 12, at 75 I'll get 8. Empty, similar deal. Over 20 at 60 and 16 at 85.
My personal thought is not to listen to the 150 crowd. Yes it's a good setup, but if you are towing more than once it twice a year, you'll regret it. If you think you'll ever get a fifth wheel, go with a one ton. Otherwise a 3/4 ton is perfect.
For gas, it will work, depends on cost benefit. If money is a priority over towing easy over mountain passes, then gas works. If you prefer towing ease, then get a diesel. I don't regret getting rid of my Chevy 6.0 gas for one second.