Chances are they are all bad/starting to fail, so It would be best to replace them all. However, if money is tight, you can just replace one at a time or one side at a time, if you wanted to spread the costs out over a few paychecks. Just remember that bad joints will cause poor alignment and tire wear, so you will want to fix them as soon as you can.

More than tread lightly. Leave it like you were never there, nor anyone else.
'90 X-cab 4.88's 33 BFG AT's, rr ARB, Headers, Ignition upgrade, cold air induction.
'91 X-cab 5.29's 315's BFG MT's, rr ARB, custom bumper and flatbed