Originally Posted by tma300
I have 31/10.5/15 kumho tires. Would I need a piston upgrade too?
Don't worry about the pistons, they don't need an upgrade for anything reasonable you'd ever do to your Jeep. So far as regearing goes, don't bother for only 31" tires. It's when you get to 33" tires that it becomes reasonable, cost-wise (about $1200), to regear to 4.88.
Your engine just doesn't put out a lot of power so if it's not enough with even 31" tires, you're just going to have to live with it or trade it in for a Jeep that has the larger 4.0L engine. Regearing it with only 31" tires would not be the thing to do, you would then have excessively high engine rpms. That's why I said that regearing only becomes a reasonable/good thing to do once you get to the 33" tire size.