Re: F250 ride quality
20" of wheelbase from short to long bed won't make much of an issue. If anything, I'd change out the shocks for some good aftermarket units. It's hard to tell when to replace shocks in HD trucks but every 60K or so is great practice. If your tires are getting low on tread, perhaps finding a good premium LT tire might help you out. Buying a good tire can make all the difference.
Firestone also builds air-bag kits. I ran one once on my old GMC half ton, just to bring the rear end up from the weight of 900lbs of tools in the bed. When I ran it empty, I kept the bags around 10psi, which was an AWESOME ride. Loaded, I'd pump them up to around 40psi as they were rated to level out up to 1500lbs of additional weight. Solid axles aren't the best for washboard cement highways anyway, but air does help.
'00 Durango R/T 360ci 290hp (modded); 138,500m
'06 Pontiac G6 GT 3.5L 220hp; 44,000m
'12 Chrysler 200 Limited 3.6L 283hp; 13,000m
'99 Taurus 3.0L 2V Vulcan 145hp; 154,300m - Traded
Amsoil in all vehicles!