[Xysting]

The game isn't just reliant on your gfx card, you also have to realize that your CPU comes into the picture.

Check your heat levels, is your CPU getting too hot? That would cause it to under-perform.

[Based God Tyrone]

Your card should be fine, I have another pc laying around with a 9800gt that is still running strong.
Clear out the dust on the heat sink, scan for virus and defrag your hard drive and close any unnecessary programs.