The tech info on the Tire Rack web site states the BFG ATs measure out at 32.7 inches diameter. I go down to Nashville several times a year with my Tracker. It is a 4 door with a 2 liter, 5 spd and I run 235 series Cooper tires on it. I don't go off road, but you are right. It is all hills in the area and shifting and downshifting is constant. Just running fire roads with 30" tires (29+" to actual 30") is doable with 4.62 gears in lo-range. Your truck is lighter than a four door. Finding a set of 4.88 gears (from an auto equipped truck) will make your truck MUCH more drivable on 30s and a set of 5.12s would be more better if you are hell bent on running 31" tires. If you decide to go larger than 31", if you can get the fender issues solved, you will probably want higher gears than 5.12s. Skyhiranger has 5.38s and 5.62s for sale. I think they are 10 bolt instead of 12, have 22 teeth sidegears in the front and are a bit pricy but higher gears are gears and bigger tires need them. 235s are a decent compromise on the loss of mechanical advantage running 4.62s. I still have a usable 5th gear. I can't imagine the loss of power with true 30 or 31 inch tires without upgrading the diff gears along the way. 5th gear would disappear at some point unless you can get the truck up to interstate speed and more into the engine power band. The clutch would start trying to pick-up the slack and lead to premature failure me thinks. It would have been nice if there were more gearing options for these trucks and they had left more wheel opening when they built them!