Think gas or diesel will get you up any hill to your satisfaction. Actually when comparing new the gas may even beat the diesel up the hill in the RAM line. I had a 5.7 Hemi and that thing pulled as long as you did not mind the sound of a screaming engine. My diesel with the tms pulls different, you never feel underpowered but you never feel over powered. The power just always seems the same if it is a flat or 7% grade.
I don't agree that your not at least in 3/4 ton area, those who say they tow just fine in that kind of weight are tring to convince themself that what they are doing is fun. They are doing it cause they do not have the option to upgrade and are too far in to say their wrong now. I have driven and sat on the passenger side of many of these "just fine" towing rigs and they will get the job done, I will not argue that, but you have both hands firmly planted on the wheel the whole way, if you don't mind that a 1500 May be an option. I camp to relax and needing to worry about the drive there and back or long trips, not signing up for that.
I don't agree that you will spend more fuel on a bigger truck. My dually diesel (2014) gets me between 3 and 4 mpg better then my 1500 did, (2011) not towing and towing, only 8 mpg better. Love it!