Hi Brian,
I think you are onto the problem...
I was able to troubleshoot over the phone with Dan Mauch (nice guy!) and we think we may have it solved. After going thru some tuning stuff in Mach2, he had me check voltages coming out of the PC (Brand new 2.2 ghz Emachine from Best Buy) thru the DB 25 cable. Hooking up meter to pin 3 (controls x axis) and pin 18(common). Going in the direction that it did not miss steps the meter read 3.2 volts.(Still too low) In the direction when it missed steps the meter read .1 volts! Dan is sending me device to amplify the DB 25 output next week. I will let you know if this solves my problem.
Thanks for listening...Danny