I may be covering something you’ve already done, but it likely a combination of worn parts. A good method to check steering components is have an assistant move the steering wheel back and forth throughout the play while you check each component.
Keep in mind the drag link has spring loaded caps that will give a little under load. Make sure you check the Bellcrank pin, mount , and the frame tube to frame welds. Check the tie rod ends for any that are loose, and then check the box for movement in the sector shaft bushings.
If it passes all those checks, it’s possible an adjustment in the box may help. But like Rus points out, you need to follow the service manual procedure for adjustment or it will cause a binding issue.