Steering help

Was recently able to drive the f150 for the first time and I noticed that I could hardly turn the steering wheel, it would just keep springing back into place. Even with the power steering hooked up, and greasing everything it hardly turns without jittering. I now know that the problem is in the gearbox, tried to adjust it and it didnt get any better. Do I attempt to rebuild or do I get another gearbox?