The most common cause for UCCNC running sluggish or slow, to the point where it is almost unusable, is because Windows had recently automatically installed an update in the background.  This is most common when using Windows 10.  CNC Drive, the makers of UCCNC software are very good with addressing these issues, however sometimes they have to wait until they even know there is an issue, which is usually when users notice the problem and contact CNCDrive or post online.  If this happens to you before a UCCCNC update is available, then the fix is to uninstall the most recent Windows update (or updates).  The following video shows you how to do this.
If this video still does not correct the problem, please email our support department at support@stepcraft.us