Micro step settings won't effect the torque very much. If the screw turns freely and there is no binding or resistance, then I'd look at the settings and motor tuning next. The symptoms you describe sound more like settings than the electronics themselves. Lower the acceleration settings and see what the max you can set before you loose steps. Start out at 5 or so. It's hard to tell in the video but I've seen acceleration settings set to high cause that issue. 15 ipm is pretty slow. I'd expect much better on that machine. The import drivers perform ok, and 425oz steppers should be plenty. Even a 24v or 26v power supply should do much better than 15 ipm. Double check any dip switch settings on your drivers power settings. and make sure you're using what matches your power supply. I've seen the dip switch settings printed on the driver that were not correct also.