If you turn the wheel with the engine off, and you see the part of the shaft coming from the box is rotating with the steering wheel, it's the box. If the shaft from the box stays still, and the shaft from the column rotates, it's in the coupler. Sometimes they are installed wrong, with the two blocks on the end of the column turned the wrong way.
The steering shaft is turning, not the box. I pulled the shaft, spline in coupler looks worn. Looked for coupling to replace, can't find one for power steering. Not sure if anything else will work, other couplings?