Should be moved to tech forum.
I had some very loose steering as well since I had the truck and either was getting worse or annoying me more so I took a swing at tightening it. That was about 4-5 months ago and has been extremely tight and perfect since then, no rebuild was necessary.
EDIT: follow the other posts FIRST. Don't mess with the box unless you're absolutely sure the loose-ness is in the box by checking everything else first. My post here assumed you had already isolated the steering box as the culprit.
I've got the saginaw, but I assume many boxes are similar. On the top is a main nut with an allen wrench slot on it. Put your allen wrench into the slot, then loosen the main nut around it, making sure your central nut (the one the allen wrench is attached to) isn't spinning. You may have to re-turn the allen wrench a bit as you go to keep it neutral.
After you loosen the main nut, tighten the allen wrench no more than about 1/8th of a turn. Then you need to re-tighten the main nut, again verifying the central allen wrench doesn't move from its now 1/8th tightened position. you absolutely do not want to over-tighten or you'll jam up your gears and need a rebuild.
After you drive on that for about 5 days you can go back and re-tighten it another 1/8th if you need to. SOmething about your gears settling in to the new adjustment.
Plenty of youtubes on the subject and, for me, it made 100% difference and haven't had a single bit of loose-ness since.