Ball joint or tie rod end/inner.

 

After jacking both sides up, the passenger side has some top/bottom movement that i can feel (very light clunk), but i can't see any movement in the ball joints. That's also the side where the tire is in rough shape. Can't see or feel any side to side movement and tie rods seem solid. At this point maybe I'll just bite the bullet and do all 4 ball joints, it's not a huge expense to give the next owner a safer vehicle.

Thoughts?

ETA: the driver side upper ball joint still has rivets, how much of a pain is that going to be? And will I need a coil spring compressor for the job?

 

I think you have found your issue, ball joints.

A light clunk is still a clunk.

 

Glad you found the problem.

Doesn't the 99 have torsion bars as well? If so, no spring compressor needed. Uppers are pretty easy, you'll need a grinder to take the rivet tops off and a punch to knock them out. New uppers will be bolt in.
Lowers can be a pain to press out, check if there's a C-clip holding it in place before you start pressing. Generous pre-lubeing with some break-free oil will help. You'll be surprised how worn the ball joints are when you pull them out. Mine had just a little play in them when they were mounted, but once I pulled them out I saw that they were COMPLETELY shot.

Moog for replacements, they'll last the life of the truck. While it's apart check out all of the other suspension parts as well and replace as needed. You'll also need to get an alignmnet done when your finished.

Bob