Nostalrius Begins - Quality wow vanilla realm (1.12)

For the most part Window mode (noborder) runs decently, but if I want to run anything else, even youtube or a movie, on one of my other monitors the game starts microstuttering. I think it's because the game doesn't have multi core support, but I was wondering if there are any tricks to get rid of these problems. Normally in window mode it stays at 120 fps, but in cities and bgs it drops to around 60 which is fine. If I play youtube, twitch or a movie on the second monitor the fps starts fluctating wildly, going from 40-90 every second which is causing the microstuttering.

i5 3550
GTX 770
8gb ram