It may not be in the transmission.
Take a close look at everything driveline and look around and shae things if you have to.
Look at the exhaust and the heat shield above the CAT.
Once you are sure it is in the transmission before I got too excited I would drain the fluid and see what you get out of there. If it has never been changed since you have owned it now is a good time.
You have two choices when you re-fill. You can use 10W-30 motor oil or 75W-90 gear lube.
Some prefer synthetic some don't your choice.
Once you have drained the fluid start looking for shavings and pay attention to the color they will tell you what types of parts are wearing.
89 2.5 TBI, 4" RC lift, 1" Booms, SYE, Adams Driveshafts front and rear, Ford 8.8 with 4:88s, BFG 33X12.50X15, and a ton of other stuff.
AF Jeep Club Tail Number 184