First, set you step and dir pulse widths to at least 5. That should make a difference.
Is this setup in inches, or mm's?
What voltage is your power supply?
You aren't likely going to get much speed out of this setup, as you have a motor that needs over 100V to work well, and you're drive can only supply half the current it needs. Combine that with a 2mm pitch screw, and it's a terrible compbination.
A motor 1/5 the size would easily outperform the one you have.