Regarding the slip at higher speed, what steps/mm do you have configured for that motor, and what speed are you trying to achieve? As your printer has leadscrews, it probably has a higher steps/mm than usual. High steps/mm can lead to 2 issues at high speeds:
1. Loss of torque at high speed due to insufficient supply voltage. Remedy is to use a higher supply voltage, typically 24V instead of 12V. See [duet3d.com] for guidance on what voltage you need. Not all 3D printer electronics boards are 24V-compatible.
2. Electronics not able to generate the step pulses fast enough. Remedy is to use faster electronics and/or more efficient firmware. Multiply the steps/mm by the speed you want in mm/sec to get the step pulse rate, then look at [reprap.org] to see what your electronics/firmware combination can manage.
1. Loss of torque at high speed due to insufficient supply voltage. Remedy is to use a higher supply voltage, typically 24V instead of 12V. See [duet3d.com] for guidance on what voltage you need. Not all 3D printer electronics boards are 24V-compatible.
2. Electronics not able to generate the step pulses fast enough. Remedy is to use faster electronics and/or more efficient firmware. Multiply the steps/mm by the speed you want in mm/sec to get the step pulse rate, then look at [reprap.org] to see what your electronics/firmware combination can manage.