I just put new upper king pins & bushings & springs on my truck -- this was after replacing both tie-rod ends and the drag link.

The passengers side king-pin had a rough rusty spot on it and the drivers side bushing was not keyed into the knuckle.

The king-pins are supposed to be a little stiff to help dampen the steering & cut down on wear and tear to the ball joints.

Of course, there are spring bushings, frame rivets, and the stearing gear mounting plate that might be suspect too . . .