With a 4.0L and manual transmission, you should have 3.07 gears and the rear axle is a Dana 35. If you're riding on tires bigger than stock, now is a good time to think about getting axles with a better ratio. 3.55 is a very common ratio in Cherokees and you just need to weld new leaf mounts on them to work in a stock MJ. try car-part.com for junkyard searching. If you're running tires bigger than 31s, nows the time to think about buying a stronger rear axle too.
Don't pay more than $200 for a Dana35 and that's if it is in perfect working order. Most of us can find them for $100 or so. And sometimes for free. :brows: