I had a problem with mine when I first set it up. It ran at max speed at anything over 2000 Rpm.
My numbers under Motor Tuning/Spindle are - Stepps Per 1175, Velocity 857.4, Accel 212.76596, Step Pulse 6.
Under pulley 4 I have mini speed 100, max speed 5000, ratio 1.
The number you want to mess with is the steps per number under motor tuning.