The Ford gas options are the 5.4 and the 6.8. The 5.4 is way undersized for a one ton truck empty, let alone with 10,000+ lbs behind it. 6.8 (which I have now) works, but you pay for it at the pump and on the hills. With my camper and all associated stuff, I have been to the floor and down to <25 mph at the top of a long hill. One in PA in particular on the way to one of our favorite campgrounds. Mileage while towing is well into single digits. A 1 MPG difference is a 10% gain at those levels, doesn't take much to make up the difference in fuel costs and break even and even get ahead on that.
As for the price premium for diesel, I am going to have to disagree with you there. 1st, gas 1 ton trucks are like hens teeth, just aren't that many out there. The ones that are out there, are cheap because nobody wants them because they are dogs.
I don't know about gas offerings in the other lines.
Cost of tires is no big deal. Talking about adding $300-400 every 4-5 years to cost of ownership. At least at the rate I go through tires.
The only real pause that I am having about DRW is driving in snow. But, I suspect it will be better than my 2wd pig now at any rate.
I am not financing this, so the only difference in cost is upfront, no interest on the difference in cost. Which, by my math is a pretty significant difference.
The people I know in the RV world universally recommend DRW purely for stability when towing 5th wheels.