Your Jeep prolly came with 4:11 gears.. and 26 inch tires. It should run Ok like that. If you add taller tires you will have less power as the tires are harder to turn the taller they are.
4:11 means the driveshaft turns 4.11 times to every ONE turn of the tire. so then a 4:88 gear will turn the driveshaft 4.88 times for every one turn of the tire.
So changing the gears can allow much taller tires and still keep the engine in it's power band.
Some guys with the 5 speed have put tall tires on their Jeep and cannot use 5th gear ..at all..ever.. Then they put the proper gears in their ride and it wakes up again.
You havn't mentioned the size of your tires.
Big Jim <img src="/forums/images/graemlins/pfft.gif" alt="" />