The motors are stalling because you are trying to spin them too fast. Possible reasons:
- the motors are too weak;
- the drives are too weak or improperly configured;
- the power supply voltage is too low and/or the motor inductance is too high;
- the mechanical load is too high;
- you are simply asking for more than your motor/drive can deliver.
Reduce the speed/acceleration and try again, then figure out what you can do to make the machine faster.