Post some good quality pics of motors and the control box and I'm sure can talk you thru wiring them correctly if they are indeed wired wrong.? It could just be Mach's setup wrong.

Any information you can give will help.

Look in Mach's menu Config/Motor tuning and tell me whats in the boxs Steps Per, Velocity, acceleration for Each Axis by clicking on the relevant button in Axis selection at side.

Also look at what native units your using IE: metric or Imperial. Again menu config/select native units. Don't be alarmed with the warning box that first pops up just click ok and then the native units will be shown.

Your problem could be that the Native units are wrong for the Motor tuning.? If the units are imperial and setup for metric or vise versa then motors will appear to judder.

Check what version of Mach your using has well by looking in the menu Help/about mach3 should see Version box.