I've got some Issues... well not me, but my car!

Ok so I pulled the drive shaft tonight and was able to inspect the U Joints. The caps fell off the rear U joint as I pulled it out. There is noticeable difference in the front and back. The front is a lot smoother with maybe some movement. (Hard to really feel any play in that one.) The back is "dry/tight" when moving it around. I mean its not hard to move around, but it doesn't move freely. I put the caps back on that fell off and made sure all the needles were still in place in them. Spinning the cap around it does sound rough! like a bad bearing. My next question is how do I know what to replace them with? On the drive shaft itself there's two different numbers on each end 2660724 and 2560724. On one U joint its has USA 108, and the other USA 300. Any help on how to look up replacement U Joints?