I think I found the problem and fixed it. It was a mechanical issue, the Z-motors are on the bottom end of the lead screws. There was a special flexible coupling between the motors and the lead screws. This coupling would pull apart if the lead screw tried to pull the Z-stage down.
I used 1/4" brass strips from a hobby/hardware store and made clips to keep the couplings together and used cable ties to keep the clips in place.
The Z_TILT_ADJUST Macro works fine now.