What width rims are you running? If the rims are too narrow, that will cause problems. I would suggest that you go to a 16" rim, then use a LT245/75/16 E load range, like what a modern 3/4 ton would use. That will give you plenty of load capacity, plus it will be a narrower tire. A 235/85/16 would also be a viable option, especially if you end up doing the duallie conversion.
