I was thinking that I might have some U-joint problems because I have some driveshaft clunks, but I don't have any loud vibrations at high speeds. I know I have a bad center support bearing so I will be taking the driveshaft out within the next week and I want to be sure I will have all the parts I need. Anyway, I got under there and check for play in the U-joints and they seemed really tight. here was some play in the driveshaft itself, however. With the transmission out of gear and the parking brakes on, there was about a sixteenth to an eighth of an inch of twist. When I put it in gear it was tight, so the play is in the differential. Is this normal? If this isn't normal, I assume this is the source of my clunks coming out of gear. If this is a problem, what would be the likely cause(s), and what are my options for fixing it?

With 165K should I just go ahead and replace the U-joints while I have the shaft out, or is this unnecessary?