Mendel90/RUMBA/Marlin - Z-Axis too slow, X, Y work great (1 reply)

Hi all -

Mendel90 printer
RUMBA controller w/A4988 Pololu drivers
Marlin firmware
Repetier software

I have calibrated motor moves with configuration.h in the Marlin firmware, and set the RUMBA microstepping jumpers under each of the A4988s to be at '000' (single step).

My calibration in configuration.h:

#define DEFAULT_AXIS_STEPS_PER_UNIT {78.7402*1.05,78.7402*1.05,200.0*8/3,760*1.1} // default steps per unit for ultimaker

X, Y and E all are moving as expected, pretty calibrated. Z is moving waaaay too slow. I should only have to tweak the 200.0 factor a bit, not increase it by a factor of 5 or 6, right?
It almost seems like my microstepping isn't right, even though the jumpers are set correctly.

Any thoughts on how to proceed here?

Thanks,
Rob