95 XJ driveline vibration

I've got a 95 XJ with 140K miles on it and a vibration that is about to drive me crazy. It occurs at speeds of 55 and above. I've balanced the tires, aligned the front end, and changed the U-joints with no success. It feels like it's coming from the rear of the vehicle but I'm not certain because the whole vehicle shakes pretty good. Maybe some worn steering component? Could it be wheel bearings? How can I tell if wheel bearings are gone? What else should I check?

You can tell if the wheel bearings are gone by lifting up the jeep and then trying to wiggle the wheels. In and Out. If there is any movement then they are shot. you don't have any dents in the drive shaft do you? I got a dent from a trail ride once and at 55 i got a vibration. When/how did it start? slowly or just out of nowhere? Plus pull your rear wheels maybe some mud or stones in the drums.

I don't think there are any dents in the driveshaft. It's never even really been off road. The vibration started slowly probably around 100K miles. When it first started it came right at 55 mph and at 65 it went away. I was close to needing tires and figured when I put new ones on that were balanced and aligned it would fix it, but that wasn't the case. Over the last 20K miles it has gotten progressively worse, to the point where I don't want to get on the interstate anymore.

I've actually lifted it off the ground to check the wheel bearings and the front wheels have no wiggle in them but the rear ones will wiggle very slightly. Is that normal?