Power steering gearbox

Make sure the play is actually in the steering box. Have someone else move the steering wheel while you observe the steering action under the hood. Things to keep an eye on:
Pot coupler- the "flex joint" at the end of the steering column where it attaches to the steering box. Is a normal wear part and rebuild parts are commonly available.
Pitman arm- the steering arm that attaches to the bottom of the steering box. Watch it as your friend moves the steering wheel and make sure the "ball joint" type end isn't showing signs of movement.
Tie rod ends, idler arm, ball joints- same test as before, look for slop as things move!
Lower control arm bushings- if everything else is performing adequately, watch the lower control arms as the steering is moved; if bad, you can actually see the control arm shifting on it's mount.
These are just basic checks and not a guarantee, but if the box was properly rebuilt, the chances are the problem lies elsewhere.