Hi Mike,
My position problem is not just a few thou. What happens is one (or more) of the axis will drop a large amount of positions, sometimes to the point of crashing the entire machine. It is rare, but still a pain. I have not had a program run over 6 hours yet, so can't comment on the precision after that period of time. I do not think it has anything to do with MACH's interpretation functions. It could be something in the computer system such as non-ECC memory or something weird like that. Anyway I haven't had a problem since turning off "Automatic Updates" and never allowing the monitor to go to sleep or screensave.
BTW - When setting the priority of Mach to Realtime, I have lost a USB wireless mouse function. I was only manually moving the gantry, but had to reboot as not even the 3 finger salute would break into the system. So beware. I am going to try some higher priorities just below Realtime.
Regards
JWI