It is unclear what you are talking about when you say “the stepper motor jumps are limited”. It sounds like you are trying to run that motor at about 2400 rpm (if your 128khz is 1/16 microstep mode), which is not likely to be practical with the motor. This thread on our forum, where someone is trying to achieve high speed operation with a similar Sanyo pancake motor, might be helpful for you:
To check your code, you might use something like an oscilloscope or a multimeter with a frequency measurement setting to verify the STEP pin is being pulsed at the frequency you intend.
-Nathan