Another to consider about gears. If you go from a stock 30.5" tire, to next generally speaking diam of 31.5 or 32.5" diam tire. Your 4.10 gear setup just went to an effective 3.95 or 3.73. So if you go to a say 285-75-16 @ 32.5", you would need to go to a 4.33 or there about to keep your effective ratio at 4.10....
More to this than tow rating per a gear ratio chart like Ben is showing. Tire diameter also needs to be taken I to account, along with what that bigger diam tire weighs, taking HP away from getting to the ground turning said bigger heavier diam tire....
Marty