Framrate drop after Alt-Tabbing

I'm not sure what is going on but it's a constant issue. If I alt-tab to my second screen (whether I'm in Window mode, Fullscreen window mode, or Fullscreen mode) and alt tab back into the game, my framerate is stuck at a lower framerate.

As an example, I will be running at 50+ FPS. However if I alt tab for something and tab back, my FPS is stuck at 20 FPS. Only way that I've found to reset is to go into the graphics setting and change the default video setting from Desktop standard (which is what I normally have it set it at) to Desktop High, and then back to Destop standard.

Pastebin link to my DxDiag report
http://pastebin.com/0B58RDYv

Ok. I was doing some research and it appears that it's a framerate difference on my second monitor that appears to be the culprit. Since my main monitor has a max resolution of 1920x1080 and my second monitor is 1440x900 the game cannot handle the different resolutions at the same time. I don't have this issue in other games I play so it is most likely a bug with the game itself that this is happening. As a temporary fix to this, I've just plain turned off the second monitor while the game is being ran.