FPS went down to 20-25 from 50-60 after installing new nvidia drivers

Hi folks i bought a new pc my spec are
i5 3670k
asus
nvidia 660ti asus dc u 2
8gb ram

i own a default asus nvidia 660 ti dcu 2 and i didnt had any problems running games like sleeping dogs or nfs most wanted and even world of warcraft it was running fine and i was getting 50-60 FPS in crowded areas like Ogrimmar and Stormwind but after installing the new drivers i noticed there is a shuttering issue my FPS goes down from 48-50 to 25! after 1 min and yes i have tried a clean install for instance uninstalling old drivers and deleting regestries by ccleaner than too i have this issue please help....