Hi,
It's not easy to say what the problem is. It might be that you need to start even slower than ~100Hz and then ramp up the step frequency, in order to see if that is the case increase the pause time between each step to something like 25ms.

The above is also the answer to how you change the speed. There's the DELAY variable which, in my example gets assigned the value of 10. Between each step there's a delay of 10ms, change that and the motor speed changes.

A schematic of how you have it wired would help too. Usually you run step motors at much higher voltage than what they are rated for and then limit the current. For unipolar drive this was usually done by big series resistors. In todays bipolar drives it's done thru chopping/PWM.

With PBP you don't need to specify anything with the NEXT statement. It automatically belongs to the FOR that is "closest to it". You CAN definitely add a variable to the NEXT for added clarity but it's not needed.

Finally, you say the motor has a step angle of 5.625 degrees, that's 360/5.625=64 steps/rev. Then you have a gearbox with a ratio of 1:64, so 64*64 is 4096 and not 2048 as you've stated....something isn't correct there but it's not related to your problem so it doesn't really matter right now.

/Henrik.