My 1991 Jeep clunks when I put it in gear..Dont they check the U joint when they do state inspections?..What else could it be?

 

Mine does the same thing, except its not the u-joint. My play is in the actual differential and the way it was explained to me was that as the gears have more miles put on them the clearances become bigger so when you put her in gear that is the clank you hear...all that "slop" being taken up only way to fix is new gears

 

doesn't hurt to get under there and check your joints.
while you're under there, check your tranny mount.
also, make sure your exhaust isn't bumping up against your cross member, gas tank or trailer hitch.