The motor data I was after was the rated current, inductance and holding torque of the X and Y stepper motors, not the firmware settings. Anyway, if your steps/mm with full stepping is as high as 141, then almost certainly the problem is that you need very high motor RPM to achieve reasonable speeds, and you do not have enough motor drive voltage to overcome the back emf of the motors at those speeds.
If you have the motor specifications, this can be calculated. See [duet3d.com].
If you have the motor specifications, this can be calculated. See [duet3d.com].