Gas will work fine.
The diesel won't help if you go to a 5th wheel because it's in a 3/4ton. A 14k 5th wheel should have you moving up to a 1 ton possibly even dually, so you won't be able to use all that extra pulling power.
My one question is what is considered bare bones today? My first truck (just a small one) was bare bones: manual windows, manual steering, manual brakes, manual transmission and no radio. I suspect this one is a bit more tricked out but that's a personal choice how much you like the bells and whistles.
Then again, trucks are a dime a dozen. If you think you might move up to a bigger trailer, I would be looking at SRW 1 ton trucks.