Try cranking the torsions and a set of 33x10.5x15. The outer edges are what hit on the cab side of the wheel wells with 12.5s. Offset rims make it worse. Remember to mark torsion bars before you do anything. If all else fails return it back. Oh by the way, you need to calculate speedo too, most likely will crap out the speed sensor in rear axle with change in tire size, see posts here say its a known problem. 32s work too.

 

changing tire size has nothing to do with the rear wheel speed sensor going out, however it will screw up your speedo if you dont have it recalibrated

 

Ok, maybe I have a tempermental truck. It did it with 31-33, then 33-35s, now with old 35s to new 35s the ABS and Brake light come and go. Chevy guys have same issue. I only have rear ABS wich sucks on dirt when nose is plowing and the rear is pumping. Oh, the no low switch on transfer case sucks too. There is no such thing as too much torque in a pull.