Did you center the steering box exactly and then set the front wheels directly ahead BEFORE making the drag link?
Sounds to me like the new steering box is off center when the front wheels are straight.
This centering procedure MUST be done as the off center slop can't be adjusted out of the box.
Steering boxes are designed to have a tight area dead center and this is where the box needs to be when going straight.
The tight spot is there to allow some adjustment as the box wears.
If you adjust out the slop with the box off center you will damage the box when you try to steer past the now too tight area at the center position.
Pictures of your setup would be good.
Why the rag joint? Would it contribute to slop?So I put it on the mount bolt it on the rag joint