Hi, Guys. I think I finally got the problem of the losing steps solved. I remembered that the Mach manual says not to use on-board graphics,and realized that while I have been using an AGP video card since I first built the machine, I hadn't checked the BIOS to make sure the on-board graphics adaptor was disabled... Duh! I went to the BIOS and set the primary graphics to AGP ( it had been set to PCI), and the next line states " Assign IRQ to PCI graphics" Yes/No. Of course it was set Yes. I changed it to No and saved the settings and booted. The computer went through some "Found New Hardware" conniptions before telling me to reboot so some of my new hardware would work... I did. When it was booted up, I checked the device manager to verify that the 2 LPT IRQ's had not changed. They had not, so I didn't have to fix anything there. I started Mach 3 mill, ande everything has worked perfectly for 2 days, now. I don't know why I didn't experience problems sooner... or maybe I just never noticed the lost steps with my one-off projects before, but I know it seems to be working correctly now.

Moral to the story: If you are experiencing lost steps in repeat operations, check that you don't have an onboard graphics adapter hogging an IRQ and inadvertantly sending step pulses to your parallel port. Thanks for your help, Don