CPU usage drop

So when I go into the game everything is fine, combat plays fine with no issues. But after 2-3 minutes of gamplay whenever I go to combat I get a cpu drop.  It seems like the computer won't use more than 41% cpu. it's causeing major fps drop and sound issues that make ir unplayable. After I go out of combat my cpu usage goes back to 80%-100%. Anything I can do to stop this CPU cap the game does?