Gecko G540 on a minitech minimill 2

[LegendCJS]

I think I know what is going on. The computer you are using to control the gecko 540 is probably newer and as a result your parallel port can't source enough current to drive the optos on the G540 with two microseconds. On modern computer parallel ports only 40 us of pulse width is long enough to fire optos reliably with the low current modern parallel ports have. Without the Sherline 1/2 stepping mode Mach3 seems limited to 15us pulses at maximum.

[KTP]

Just add a buffer chip between the parallel port and the G540, then run whatever pulse width you want and the buffer chip will drive the optos in the G540 with plenty of current.