Link to the kit?
Have you run drivertest.exe in the Mach3 folder?
If they are cheap drives, you may be getting resonance issues. You should have them set to 1/8 or 1/10 microstepping, but even then you may still be running into resonance issues. I have dampers on my steppers, to get rid of the resonance.
At 24V, you won't see much speed out of that system with 1/2-10 acme. Best case is probably 50-60ipm?