Some of todays new gas trucks have 400hp and can get over 20 mpg, 15 towing, I am and have been a diesel man but it is because of how much I tow when farming, gas truck just won't do it .
my truck gets 13-14 mpg pulling a 7,200 lb TT, and maybe high teens when empty on a good day.
My opinion is you mite be better off with a 6.0L or 6.2L gas full size 1/2 ton 4x4,
my co-worker has a 2016 GMC 1/2 ton 4x4 with the 410hp gas that gets 24-25 unloaded all day @ 65-70mph, he is a salesman and puts on a lot of miles, no idea how it tows but I would think it tows nice.
I have also found myself needing fuel and having to search for it when passing many gas stations.
I would buy one in a second but momma says my old Dodge would need to go and I just can't let it go.