If you still have play, then you need to remove it. If you can adjust the box, then you to do it.

Also, don't overlook the rear suspension. Loose members can cause the car to exhibit strange handling characteristics. Start by raising the car and examining all the bushings in the "dogbones." You should see no rubber pieces coming out of any of the joints. It never hurts to grab them and give them a shake to check for looseness.

Hope this helps,