I'm having a similar problem. Connecting usb directly to drivers and running motors they are perfectly smooth. Connecting thru controller and running mach 4 they stutter. I've tried every motor tuning configuration I can think of and get somewhat better results but the jerkiness or stuttering remains. I'm going down the computer route as well. Going to do a fresh install of win7 and hope for the best. If you do solve this. please post what fixed it.