Ball Joint
Before you have it done, check to make sure its bad. Jack it up by the axle so the tire is a couple inches off the ground. Find something to use as a prybar, about 3' long. Slide it under the tire to pry the tire up in the air. New joints will go in and out a little. GM actually allows for 1/4"! I allow up to 1/16". If they say its loose, thats where you'll see it. They can cause more steering problems by drying out and rusting up. That makes them real tight and wear a spot centered so the wheel doesn't want to turn.
Good luck,
Dave