No F350 ever came with a C4 and the C6 trans was long gone by the 2000s.
You don't need 19.5 wheels and tires and you won't be slow on the hills if you don't want to be.
We had a '99 at work with an exhaust and a tuner that used to FLY up the mountains with more weight than you'll have. It was sold last year with 240,000 very hard miles (work truck) and still ran great.
I'd go with the bigger camper. If you're gonna live in it, the biggest one won't be big enough, and your truck will carry it. I carry that much weight plus a 9500 trailer with a '99 Dodge with no problem.
I added airbags, sway bar, a "built" transmission and tuner - the usual stuff of a well-set-up hauler truck. I live in my 11.5 footer (with my wife) for about ten straight days each year and going to a shorter model camper just isn't an option.
I know a guy with a '99 F350 in his work truck fleet, a single-rear-wheel, that weighs 12,000 pounds at all times. The thing is a reliable work horse. Don't listen to the people who say you NEED a $75,000 new truck.
Heck sometimes I still haul my large camper plus very heavy trailer on my completely stock 1986 GMC, with no problem. It's just slower, which I could fix if I felt like it.
They'll also tell you you've got less payload if you have 4WD and/or a diesel, because the books say so. Technically that's correct but in both cases all the extra weight is up front. Virtually all your load will be on the rear.
