problem with gecko 201 dirve and cncpro

Hello,

I posted a message about this problem a couple of weeks ago, and
have since had a chance to do some more research. My configuration
is a sherline 5400 English milling machine, 3 gecko 201 (not the 'a'
version) drives, two powermax II stepper motors & one sherline
stepper, and an XT computer running the latest version of cncpro.

There appears to be two problems:

1) The steppers are 1.8 degree per step, and I compute this should
be 40,000 pulses per inch (the gecko is a 10 microstep drive).
However, it's taking approximately 52000-53000 pulses per inch.

2) There is some kind of accuracy problem that I'm having trouble
quantifying.

Since problem #1 seems easier to quantify and more obvious than
problem #2, I've decided to tackle it first. Yes, my machine _IS_
the 5400 english model, and not the metric model. I've verified
there are 20 rotations of the handwheel per inch.

I've tried two different computers, a handful of parallel IO cables,
and different parallel IO cards. I've also tried building and
installing a buffer board to boost the parallel signal for driving
the gecko's optocouplers. None of these attempts has produced any
change.

As a side note, I am getting some occasional humming from the
motors, and only when the computer is connected (this led me to
build the buffer board I mentioned above, which did reduce the
humming, but did not effect the positional problems). The humming
only occurs at certain phases where the motor is stopped.

Does anyone have any clues as to what I should look to next?

Thanks,
Scott