Drag link and center pin are normally the 2 main culprits. Also make sure your tie rod ends are in good shape.
If you climb under it and have someone turn the steering wheel, you can watch all the various parts moving. It's fairly easy to see where the movement is either not occurring in sync with the rest of things, or where things are going up and down instead of side to side. The up and down will most likely be seen at the drag link and/or center pin. Up and down is bad, side to side is good.