Hi Terry,
Just my thoughts...
If the Z axis DRO continues counting down while the axis is on walkabout then the chances are that the problem lies in your Gcode.
If the Z axis DRO continues counting both up and down while the axis is on walkabout then I would suspect that the axis direction signal is not being properly recognized by the controller.
If the Z axis DRO stops counting while the axis is on walkabout then you need to look at your driver hardware.
Tweakie.