Thanks ronjenx, for writing this out for us.
Finding Your Gear Ratio
Here is a procedure to get the axle ratio when it is not known. Build sheets (available from your dealer, or from the Jeep web site) will only tell you what the Jeep had from the factory. A used Jeep could have been re-geared.
If you want to know for sure, and remove all doubt, do this:
Chock the front tires, fore and aft.
Put the transmission in neutral.
Emergency brake off.
Jack the left rear tire off the ground.
Put a jack stand under the frame, just in case the jack fails (had to add this).
Put an index mark on the aft end of the drive shaft, visible from the left rear wheel.
Put an index mark on the left rear tire at the 6 o'clock position.
Rotate the left rear tire 2 complete revolutions while counting how many times the index mark on the drive shaft passes its original position.
That number will be your axle ratio.
Remove jack stand and lower jack.
Put transmission in gear or Park, apply emergency brake.
If you have limited slip, jack up both rear wheels and rotate one revolution, making sure both tires rotate equally.
If the drive shaft rotated almost 3 1/4 turns, you have 3.21
If the drive shaft rotated almost 3 3/4 turns, you have 3.73
If the drive shaft rotated a little over 4 turns, you have 4.10
If the drive shaft rotated a little under 5 turns, you have 4.88
If the drive shaft rotated a little over 5 turns, you have 5.13
Now go drink a beer and feel confident that you know your gear ratio without a doubt