Just from the sound of what it's doing, I would say that the sector gear is not centered properly on the worm gear. Most likey, it's too high up on the worm, and is hitting the end of the ball track when it comes back to "center". Posibly the steering shaft got turned when you had it apart. You might try taking the pitman arm off, center the box, then re-install the pitman.

Bill Burmeister