Vibration woes...

Over the past few weekends I have been trying to diagnose a vibration I have in my truck...

The shake started after I installed an RCX 5" lift and 37" cooper st maxx's. At first I thought my tires were balanced incorrectly as I had an extremely hard time finding a place willing to attempt to mount them. The vibration is not severe and it is not DW. Its more of a bounce felt thought the whole truck. I don't feel it in the steering wheel and I don't really feel anything that has the same rhythm in the 4x4 lever (but I do feel it move as I use the skinny pedal and hit bumps). It really only noticeably shakes at speeds greater that 60mph, the shake is not constant, and does not seem to have any particular cause at it comes and goes for various amounts of time and intensity.

I have worked through everything up front, bushings, bearings, ball joints, track bar, pitman arm... THE WORKS

I now have to start looking at the rear. Today I jacked the rear up and ran some tests at various speeds up to 90. I get a SLIGHT shake similar to what I feel on the road at various speeds 60-90mph both accelerating and decelerating. I also did notice that the tired are not perfectly true to rotation, but im going to assume that's normal and I would feel that shake all the time and would get much worse as speed increased. I have not really shaken anything under the truck as of late because I park outside in the snow on dirt... yada yada its cold!

Does anybody thinks its worth my while to pull the drive shaft and replace the joints?