X1900 GT HELP!

[ULTIM@TE_GAMER]

Ok so I have a X1900 GT and I have been having some trouble with the drivers. Basically I had to uninstall and reinstall them about 4 times. Somewhere I think something got severly screwed up since whenever I start a gamming app or run a 3D test the thing always is fine and then it starts to severley lag. Like say it was at 30 fps then it would be at like 2. This is a big problem for me the only thing that confuses me is that during normal operations such as word and itunes .etc the thing never has a problem. I know it is not the graphics card since when I first installed the driver it was fine.

Do any of you guys know what is happening or had similar experiances?