The Duratracs are very wide, the 235/85-16 size will leave you with less than 1/2" space between the duals (just measured them). General Grabber AT2 are slightly narrower, so they do fit a bit better, and they are quite excellent in SRW application but not so much on a nose-heavy dually diesel 2wd (same exact truck with 4x4 and limited-slip diffs is darn near unstoppable tho). Not sure how wide the Cooper AT3 are in that size, but they are not all that aggressive tire - they are actually quieter on the road than the Grabbers and way quieter than the Duratracs, great all-around tire but I wouldn't expect it to pull you thru a wet field (if that matters to you).
I'd say if you're not stuck on the 235/85-16 size, drop down to the factory 215/85-16, but naturally in load range E (think the door sticker calls for D-range, to heck with that). Those can haul almost 2500 lbs each when in dually application, makes for near 10k axle capacity - should be plenty strong (certainly way better than factory), and allows you to run whatever crazy-gnarly tire you happen to like. Add a nice heavy load at the very end of the bed, and if you have a decent traction device in the axle you'll be able to go thru some places that before got you stuck just by looking at them.
