It would transform your driving experience on your Jeep! It would really launch much stronger right from a stop, and remain much stronger all the way to whatever the speed limiter is set to.
On the street, your upshifts would occur at lower speeds. For example, if your 1st to 2nd upshift (at full throttle) occurs at 40mph, then after the gear upgrade it would occur at, say, 31mph. If your 2nd to 3rd upshift occurs at 70mph, then after the upgrade it might occur at 58mph. This is because the engine is revving higher and approaching its rev limit, and the computer upshifts it to the next gear.
Of course, all this is very general since we're not talking specific ratios.
Offroad, the change would be most greatly enjoyed! The raw torque, especially for rock- and stump-crawling, would be greatly improved. With much lower throttle inputs you could still crawl over anything, which equates to much better control over those tricky stumps and boulders. Your crawl ratio would be far more respectable.
Transmission 1st gear X Transfer case low range X Gear ratio
Example with 3.73:1 gears: 3.00 x 2.72 x 3.73 = 30.4:1
Example with 4.10:1 gears: 3.00 x 2.72 x 4.1 = 33.4:1
Example with 4.56:1 gears: 3.00 x 2.72 x 4.56 = 37.2:1
Example with 4.88:1 gears: 3.00 x 2.72 x 4.88 = 39.8:1
You probably have a Dana 30 front and Dana 35 rear axle? I know for a fact that you could get 4.10:1, or 4.56:1, or even 4.88:1 ratios for them. For some other model of axle(s), you'll have to make some phone calls. Superior Axle & Gear has been working on Jeep gearsets for years, though I'm sure others have them as well.
Remember that if you have a 4WD, then you'll naturally have to upgrade both axles to the same ratio. (Some offroaders deliberately install a fractionally different ratio front-to-rear, to provide a little torque bias for offroad use.)
Do some regular web searches on "Jeep Dana" and "Jeep Grand Dana" and other phrases like that -- tons of great info.
Here's Superior Axle & Gear's contact info:
Superior Axle & Gear
3954 Whiteside St.
Los Angeles, CA 90063
Phone (888) 522-2953
Fax (323) 268-9085