Hi TOOL MOR. It's a FINE first post. Welcome to the Zone!
That's a lot of backlash. There may be something loose somewhere. Check everything in your Z axis for tightness. Put a block of wood under the head, lower the head to rest on it, and adjust the Gibb.
Check the coupler grub screws. Make sure the motor is mounted securely to the column plate. Check that all bearing mounts and head screws are tight. Tighten all of the ball nut screws. Make sure the column bolts are tight.