GP4 Running Really Bad and CPU Occupuncy

I have recently upgraded my computer from:
AMD 64X2 6000+
8800GTX
2GB of Ram.

Running under Vista 64 I used to get about 50fps when running the game in 1280x1024 with everything maxed out completly.
But I recently switched to:
Intel Q9550 Quad Core
ATI 4870
8GB of Ram

Again using Vista 64 but this time I can only get 30 fps and the game jerks so much when driving past the pits and in trackside replays.
I have also changed the resolutions and it runs the same in 640x480 as it does in 1600x1200.

I have tried running as admin and in Windows XP compatibility mode and no matter what I seem to try the game just wont run properly, is there anyone with the same graphics card having problems like I am?
I also have the CPU set as 1 in GPX Patch.
I also running carsets in CSM, mainly the 1991 patch.
The processor occupuncy is also running around 150-280.

Any help would be appreciated.



Edited 1 time(s). Last edit at 12/16/2008 10:42PM by bsmaff.