Diesels are nice but would be overkill for what you are asking IMO. Unless you go to one of the new smaller ones but I am not sure what their capabilities are. Will you get 35% better mpg NO, but you will feel happier I guess.
You have a 17, pulls what you want and you seem pretty happy. Check and see if there is a regear option available that would help some.
Chebby has the v6 diesel, cummins is avail in the titan, not sure if dodge is getting a smaller one and the f150 is coming out with a v6 diesel I think. My SIL has a v6 turbo from ford and it pulls his TT just fine with 3:73 gearing.
I would say unless going to mountain all time a gasser like yours should be fine, diesel and probably the 7.3 overkill unless you plan to go bigger soon.