2nd monitor window animation lag

Hi everyone, title says it all- my 2nd monitor randomly starts lagging with window animations (open/close file explorer, etc.) And its extremely annoying. Drivers are as up to date as possible. System is an XPS l502x with an i7, 6gbs ram and gt 540m and the second display is a new 21.5inch 1080p dell. It looks like the Intel powers the main display and the gt540m powers the external through the HDMI so it shouldn't be shy on power. Any help is appreciated.

Thanks!