What gears do I have in my Jeep?
I4 Automatic - 3.73:1
I4 Standard - 4.10:1
I6 Automatic - 3.54:1 (normally)
I6 Standard - 3.07:1, 3.54:1 or 3.73:1 - must verify with the tag on the axle or by pulling the differential cover and reading the numbers stamped in the ring gear or by counting revolutions of wheel versus driveshaft.
This is from the FAQ section. Many people run those gears (4.10:1) with 33" tires, although highway will not be the best.
Herculined, MC2100, Nuttered, 31" Mud Rovers