The u-joints are mounted at the ends of the driveshafts - they are the "joints" that connect the driveshafts to the axles and the transfer case. They are small (4" crosses) - if your front driveshaft is wobbling then you quite possibly do have a bad u-joint or two in that shaft. Those u-joints would need to be removed and tossed so some new ones can be installed. If the vibration hasn't gotten worse in 30,000 miles though I would say you have another issue. Don't know what, however.
I think what you described, "long u shaped shaft, above the ear axel running the width of the car" sounds like the rear anti-sway bar - I don't know what else it could be off-hand... but if you misidentified an anti-sway bar as a u-joint you might want to have someone else work on the problem for you... no offense.
Sent from my "two hands on a keyboard"