I have a 91 Z and I think the U-Joints are going bad, but am not sure. It has a vibration in it whenever the engine is at about 2500-3000rpm in drive. I checked my tires and had them rebalanced, and I checked to see if the weights were still on the driveshaft, which they are. It kind of makes a clunking? sound when you put it in gear, and sometimes a squeaking sound. A buddy of mine told me to get under the car and try to rotate the driveshaft to check the u-joints, but it seemed solid, like nothing was loose. Any help drivetrain guys??? If it is the U-Joints, are they hard to replace ? Any help would be greatly appreciated. Thanks guys.

A squeekign sound when driving real slow, kind of like eek-eek-eek-eek several times per wheel rotation? If so then you definitely need U-joints. You can't really check them by hand.

They're not terribly hard to replace, except that if they're the factory ones, they are retained by plastic that's injected into a ring around the cap and the yoke. For that you need heat, enough to get it hot enough to melt the plastic and for it not to solidify back while you get the caps out.

A typical trans or rear end type place, or a driveshaft place, can do them in a matter of minutes.