Make sure frame skip is set to 0 in your options. If that doesn work, you can try setting your affinity in the task manager after the character select screen.
You'll need to be in windowed mode as fullscreen crashes your game if you alt tab. Head to processes in the task manager, find and right click psu, click go to detail. you'll be sent to the detail tab with psu hovered, right click it and select set affinity. Make sure everything is checked and click OK. You'll have to do that every time you launch the game.