testing vibration

A month ago my jeep started to develop a vibration that was only felt at certain speeds (especially around 50). I figured my wheels just need to be balanced because it didn't really feel like a driveline vibe and the front tires have been wearing down pretty rough (btw I have a 3" lift on a 1998). But after getting the wheels balanced the vibe still happens. So I figured it's time to check to see if it's the driveline.

So my question is, would it be safe to check it by jacking up a rear tire and bringing it up to speed to see if vibes still happen. Also, can you think of anything else that could cause the vibe (i.e. misaligned brakes....)
Thanks in advanced.
-Darren

3" lift ... vibrations at about 50mph ... me thinks you are experiencing the symptons of a Jeep that needs an SYE. Or it could just be because you have bald tires...but I'm betting more on the SYE. Especially being the 98...you've probably got the 242 with a 8.25? That's about the worse case scenario for having a lift without an SYE.

yeah thats what I'm suspecting after the balancing didn't do anything at all. (previous searches here lead me to believe vibes around 50 normally means unbalanced wheels). But I started to get uneven tire wear (plenty of tread left) when the vibes started. And yes I do have the 8.25/242 lovely setup haha. I've been planning on the h&t anyways, but right now i just want to pin point where its coming from before I go back to school.

Usually balding tires will give louder road noise, but I ran my Cavalier's (when I had it) down almost to the metal and it never had any vibrations, just very, very loud. And since balancing didn't do anything........sounds like you'll have to take the next step....

u-joints? Did you grease them ?