I did increase clock frequency to 700-something. Two are plugged directly into mobo and one in USB on front side of comp. I'll try to go back to stick and see if they can work uninterrupted for couple days at least. This is on Windows 7 computer.
Windows, by default, disables USB ports when it sleeps or turns off certain things. Try to disable USB sleep:
https://superuser.com/questions/309689/how-to-keep-external-usb-drives-from-sleeping-windows-7You have to uncheck the "Allow the computer to turn off this device to save power" for each USB port you have
Also, its possible the standard USB ports can't provide enough power.