This tweak will only work with Nvidia gpu's with an nvidia detonator driver. It can be downloaded from http://www.nvidia.com/content/drivers/drivers.asp .
We are going to need the windows registry. always make sure you make a backup of your registry before you are going to edit it. Open your registry by pressing the start button choose run and type regedit.
Start > run > regedit
while in the registry find
click on the NVTweak folder you now see and create a new Dword value name it CoolBits (make sure you use a big C and B) one's created open it and make the value 2 (hex or decimal)
This was the tweak. You can now go to your display properties select advanced in the settings tab and then go to your detonator there you would find a new function called clock frequencies.