Dead Space 3 Low Frame Rate PC

I recently aquired Dead Space 3 through the humble bundle and when I played co-op with a friend I then noticed a very low frame rate that seemed to be locked at 30 FPS. I then turned off V-Sync and reached frames well over 200. Although I was experiencing plentiful frame rate drops that would drop to 20 FPS or lower. I also noticed these frame rate drops were before and after dialogue. My PC specifications are Intel i7 3770, GTX 660ti 2gb, 8gb of ram, and running on Windows 7. Thanks.