if it was what i think it was the problem you're having right now was bug that comes with the latest WHQL driver. the latest beta should fix the problem. the gpu usage increasing up to 98-99 percent but the clock speed was reverted to idle state hence the low frame rates. it was problem known to factory overclocked cards with the latest WHQL installed. nvidia states that the problem has been fixed in the latest beta driver. just make sure you did clean install driver when updating your drivers.
apparently has been fixed. I'll continue testing this weekend. thanks