Probably need more info.
What rate is your parallel port set to and what is the max frequency of your drivers?
If you are micro-stepping at 10 and those are 200 step/rev motors with 5tpi and a 2x reduction thats 20,000 steps per in. So if your parallel port is set to 25kHz, that's pretty close to 60 ipm. And 36V probably isn't the most efficient operating point of those steppers, depending on what configuration you are using.
If i did that right...