You can test rapid rates by either simply jog back and forth the maximum distance for each axis to see if it stay in sync, or run an air carve with maximum feed rate set, and see if it return to zero.
Thankās Haldor, I donāt know where to set the feed rate yet, but I am learning a lot on here, I will look it up and give it a try, one thing I donāt understand is how the machine was returning to work zero until I put the new stepper motor on, I did not alter the settings in GRBL to $110=8000, I donāt know what setting it was before,or maybe it was set at $110=8000 to suit the old stepper motor ?