z axis doing a little dance.

A short video of the issue https://drive.google.com/file/d/1lPr...ew?usp=sharing Anybody have ideas ? I have tried all I can think of . the machine is obviously a 6040 running on Mach3. as a summary of what I've tried , isolating the Z axis ( removed everything else connected to the control box), ensured solid connections with a fluke multimeter along the entire circuit from the pulse/Direction signal wires all the way to the motor. replaced the USB control board (cheap Chinese bitsensor board )and out of the need to keep the little hair I have left replaced the cheap Chinese stepper motor driver and underpowered stepper motor with a cheap Chinese hybrid servo (Rteligent T60). I am open to suggestions .Thanks in advance.