Voltage as in your cpu clocks?
Perhaps try the settings, muck around with AA, up the detail a bit and see if can get the gpu working more.
What resolution are you in? 1080p is my guess but checking.
Are options in Nvidia CP more or less standard from install? Besides performance and vsync, nothing else quality wise set too high?
Apart from game and Nvidia CP settings which might make a difference could try another driver (Newer or older) as drivers may break performance. Not always but possible. Always clean install though just to be on the safe side, even if you need to redo a few settings.
Another thing to try might be to turn off or on cpu's Hyperthreading and see how performance compares.