Draft a friend. Stick him in the drivers seat, turn the key on, but, don't start the engine. Open the hood. While you friend rocks the steering wheel back and forth, just enough to BARELY influence the front tires, YOU look for where the slop is. Might be the rag joint, might be the steering box, or, any of a number of other parts, listed above. Once you know where the slop is, you will know what ya gotta do.
If it is the box, at one time, I had seen a really good tech article on how to adjust them up, but, it required removing the box from the truck.... I will see if I can dig it up again.
it is. This is just some diagrams, but, it shows how to adjust the box. Should give all the info ya need, 'cept for the R+R the box.....