I have 30" x 9.5" kumho m/ts with a two inch lift and they don't rub at all, but with no lift they would definately rub over bumps and if you had a large load in the back.
I had the same problem. I would be driving down the road and it would randomly shut off. I took it to some lame mechanic to hav it fixed and they knew nothing and charged me to replace some vacuum hoses. Then i took it to the jeep dealer and they knew right away that it was the crankshaft...
Is the stock rear bumper on their or if it is an aftermarket how much would you want for the rear bumper? I would take either because my stock one is bent.