Okay I am really getting frustrated. I bought my Jeep with 4.5 in lift and a set of chopped up 32's on it. It had a vibration from day one. I just figured it was a combination of the tires and needing a SYE. I recently put a set of 235's with rims on it, installed the SYE, put in a cv driveshaft, and put in a new 8.25 rear axle (I was underneath and noticed the rear diff was about 100 degrees hotter than the front. Drove it a few times and checked, it was always hot. Figured the bearing were dying.) I put the tires on, axle in, and SYE in, and was driving it in fwd (no rear driveshaft.) It was cured. When I put the cv driveshaft in the vibration came back. I tried a different one and it was still there! I don't have a clue what it could be now. HELP!

 

either bad u joints or the pinion bearing could be shot also the rear tcase bearing might be bad grab the output shaft and try shaking it it shouldnt move if it does then the bearings are bad same thing with the rear pinion grab the yoke and shake it shouldnt be any movement

 

were both driveshaft's greased? it might be a weird coincidence that they both had bad ujoints.

 

I think I found the problem. I was checking the driveshaft angle and pinion angle. I noticed the flange is wore out. The tabs that hold the driveshaft centered are worn. It looks like its enough to cause a vibration.
The axle I got from the junkyard didn't have a flange on it so I transfered my old one. I had forgot about that. I guess I should have looked it over good before I put it on the new axle.