Re: Turtle Top (like Chinook) 4x4 2006 E-350 25K, 33K miles
Duallies help in some situations (anywhere lower psi is good) and worse in others (narrow clearance, and bad ruts primarily). They are great in snow, but can be a handful when rutted out slush re-freezes.
Biggest problem I ran into is with the front tires. Dually tires are narrower, and you putting wider tires on dually rims makes for poor on-road handling due to sidewall flex. The narrow front tires just didn't have enough float on soft terrain. And, my front end is pretty heavy, and this was causing the outer edges to wear out early.
My fix for the front was to convert back to SRW-offest front hubs, which allow me to run SRW front wheels that are 8" wide instead of 6" wide, which allowed me to bump the front tire width up to 265's (and 235s in the rear which are the same height).
Swapping hubs is easy on stock Fords, but older quigleys had custom quigley rotors so that could make it a more $ ordeal. I carry a hub adapter on my spare carrier, so I can run a dually spare up front if needed.
2000 E450 dually V10 wagon