Another thing to look at are the king pin/bushings. While the wheels are in the air, grab the tires top and bottom and see if you can rock them in or out at either top or bottom. If you can you may have worn king pins and bushings.
Also, while the wheels are off the ground, check the wheel bearings for play. By rocking the wheels top and bottom for king pins, you can also tell if the wheel bearings may need adjusting.
You can see if any of the steering linkage is loose while the wheels are in the air too. Have some one grab a tire by the front and back and move them back and forth to make the steering linkage move. Watch as they move the tires and see if there is any play in the tie rod ends and the drag link. You can also have someone move the steering wheel from right to left in small arcs to see if anything is loose.
