Sounds like it may be the drive shaft is out of balance or may have a joint starting to bind up. there is a way to balance your drive shaft yourself . one is the use of a strobe light tool the other is the old school way trial and error. I'll give you both and notice the video one what you should check before tempting to balance ; check the u joints first and run out.
You will need several deferent weights, can be pieces of drive shaft, sheet metal, etc., atleast 3 hose clamps, and an um balanced drive shaft.
1) Put all 4 corners of axles up on jack stands (no not 2, but all 4--- don't need a faulty transfer case moving the Jeep)
2) Remove wheels
3) If doing rear drive shaft, remove drum brakes to avoid interference
4) Put transfer case in part time (just to avoid damage)
5) Remove front drive shaft (or rear if doing front)
6) Mark drive shaft every 25*, numbering the positions 1-4. Do this at the end near the transfer case, the part in front of the slip shaft, and in front of the yoke going to the rear deferential.
8) Start car, let it idle down, and put it into drive (WHILE PERFORMING THE BALANCING, DO NOT TOUCH THE BRAKE PEDAL. PUT A BRICK UNDER IT IF YOU MUST). Slowly climb in speed... noting where vibes are most prevalent.
7) Staring at the first set of 1-4 marks, find the position and weighs that minimizes vibes (you may not need weights at this place). Secure weights with a hose clamp.
8) Work your way down the drive shaft until vibes are minimized. You may not be able to get rid of 100% of the vibes while on the jack stands, but you also may not feel them on the road.
9) After you are finished mark where the weights are and either have the weights welded on or tighten down hose clamp. Do not remove weights.
It took me about 3 hours to do this, but I am 100% free of vibes.