Bport CNC Series 1 BOSS Quill problem

Has anyone had any problems with the Z-axis motor not working
properly. The machine just started acting up. Cold starts have not
revived it.
The Z-axis will make .001 steps OK (quill moves up and down)
.01 - it will move but in a stuttered motion. This is the most
motion I can get without problems.
.1 - the motor stutters and you can hear the Z motor 'torque slip'.
Like it does not have enough power to overcome the movement of the
quill. With the belt cover off I can see the belt gear stutter but
not move.
1 inch and JOG - forget it. It is not happening at all. Just more
of the z motor slipping.

The autolube is working properly. The quill is getting lube.
Fuses are OK. If fuse blew there would be no Z axis motion at all.
With power off to the machine I can turn the belt gear and move the
quill up and down manually.

Any suggestions or anyone know ehat the problem is??
mc_n_g