The best thing you can do before buying any gears is to play around with a good gear ratio calculator. Here is the best one we use here:
http://www.grimmjeeper.com/gears.html
You'll need to put in all of your information. Here is a run down:
You probably have an AX-5 transmission. This was exclusive to the 4 cylinder TJs and has different ratios than the AX-15 people talk about for the 4.0.
You have a NP231 transfer case.
No underdrive.
Gear ratio: Play with this number. 5.13 is what I recommend; you can compare it to your stock 4.10s or other options like 4.88 or even 4.56 (not recommended).
Tire size: enter either your current or target tire size based on what results you want to see. Subtract 1" from the tire diameter (e.g., put in 32" for a 33" tire) to account for tire deflection. (A more accurate measurement is to use the revolutions per mile listed on your tires specifications.)
Then take a look at your results. Some things to note:
The engine puts out maximum torque at 3250 RPM. The closer you can get to this RPM, the more torque you can efficiently put to the ground. If you can target this for freeway cruising in the top (5th gear), that would be ideal.
The engine puts out maximum power at 5250 RPM. Redline is about 5500 RPM. Ideally you would have a gear in the range of the maximum power RPM at the desired speed to climb hills as fast as possible.
Plugging in 32" tires (33" nominal) and 5.13 gears gets you very close to ideal in those scenarios. At 65 MPH, you'd be running about 3000 RPM in 5th, 3500 RPM in 4th, and 5100 RPM in 5th. So you'd have a good cruising gear, a good intermediate gear for towing and hills, and a power hill for passing and climbing hills.
Keeping 32" tires instead of 33s (plugging in 31") brings you even better results. At 65, you would be running 3100, 3600, and 5250 RPM in 5th, 4th, and 3rd respectively. So you have gears close to both peak torque and peak power, plus an intermediate gear.
A note about peak torque and power:
Engines are generally most efficient at generating mechanical power at full throttle at peak torque. Hence why that metric is so often used when talking about frequent hauling. At a given road speed, you actually deliver maximum torque to the ground at peak horsepower, because even though the engine isn't producing as much torque above peak torque RPM, the gear reduction more than makes up for it. Above peak horsepower, the drop in engine torque becomes so significant that the increase in gear reduction cannot keep up. Generally automakers set the redline as the point at which the engine stops producing useful power when compared to lower RPMs. Since we don't have CVTs and instead only have 3-6 gears, this is set somewhat over peak horsepower RPM. With a 5 speed transmission at a given road speed, I would say that the gear that gets you closest to redline is probably going to deliver the most torque to the wheels.
Here is a handy chart:
View attachment 204738
The closer you are to peak torque, the more efficiently you will move when the pedal is floored. The closer you are to peak horsepower, the more propulsive force you can deliver to the ground, and the faster you can accelerate or climb a hill.