We have a '93 ZJ with V-8. The Jeep is 12 years old with 90,000 miles. A couple of years ago it started to have a roughness that comes and goes. I have eliminated tires and balance as a source. Also the motor mounts have been replaced. Now I am looking at the U-Joints as a potential. Although the service manual says they are lubricated for life, what is life? It seems like 12 years and 90,000 miles would justify taking them apart and re-lubricating them.
There is one other thing after U-Joints. The Jeep dealer said there might be a problem in the torque converter. Don't recall what component was suspect, but it was not an inexpensive repair.