So you have swapped motors, wires, drivers.
The only thing left is physical, or speed related. Are you moving that with the screen, gcode, or repetier?
I am willing to guess you are using the screen, it is not tuned very well for large manual movements. use repetier and make sure your speed setting are slow enough.
The best way to test it is with gcode or a test script. I have a torture test script here in the forums. those things are set by default for tiny little 3d printers, not a relatively massive thing like the mpcnc.
I think if you run some actual gcode you will have no issues. Strap a pen on that thing and follow the estlcam walkthrough.