Z axis Stepper Motor

I have been having a problem with my z axis stepper motor for several months now. The motor would just stop working ever once in a while. The only way I could get to work was to disconnect it for the harness or at the control box. This would happen every week of two and I would repeat. Today when I ran something the z axis depth changed, I had it set for a depth of .5 inches, but it cut to a depth of .75 inch. Re-zeroed everything and retried, this time it cut to almost 1 inch. I unplugged it and it started cutting at the correct depth. Does this sound like my stepper motor going out.