I notice a friend of mine has Mickey Thompson ATZ in a 245/70-17 on his 04 dually. You might also get away with a 255/65 or 255/60, but do not quote me on that one.
hell i run 285x70R17's on all our dually dodges.
8 of them been running for no problems. already ran two sets of 285's under them. (about 80k on them, both sets per truck).
not good having the sidewalls touching creates tons of heat and surprised you havent blown one yet 285s are good one of my friends has an 04 with 285s but its got wheel spacers and looks really good