The factory service manual covers the adjustment procedure and you must follow the procedure to correctly adjust the box, or you might just damage it beyond repair. If you just tighten the small adjustment screw, without first adjusting the large nut at the bottom of the box, you run the risk do doing damage to the chrome balls inside the steering box. If it is tightened too much, when you turn the wheel, it will bind, cracking the chrome plating on the balls, and the small pieces of broken chrome will chew up the gears inside. The shaft is egg shaped, and this adjustment must be done when the shaft is located in its highest point of the "egg". In many ways, it is like getting the adjustment of the gears in the differential set properly. If you don't do it right, you will destroy the rear. Same for the steering box. I have taken many steering boxes apart, only to find that they are junk inside. When I see the screw screwed down tightly, I know that there is no salvation for the parts inside.
Also, worn or incorrect parts of the front end can also cause wandering, and adjusting the steering box will only mask those worn parts for a short while. I had a problem with one of my cars with wandering, and it turned out to be a defective idler arm. Replaced the non GM part with an original NOS part, and problem was corrected.