Hi all, this is really driving me crazy.

Don't know when it started but here is my problem. After I pause a game by pressing P and I resume by hitting P again, the game slows down and drops to about 66%. The only way to get it back to normal is by pressing tab to bring up the MAME menu and then hitting tab again to exit the menu. Sometimes I have to pause the game a few times for it to happen and it seems to happen pretty consistently if I pause it for over 10 seconds rather than pausing and resuming quickly. Any idea what it could be?
I'm on .160 my hardware is Intel i5, 16GB Ram, EVGA GTX 970.