Something may be up on the AMD side...been reports of issues with their last couple generations of cards for some time now specifically in the scope of DX9.

Just to rule it out, might want to check your clocks against reference design, verify your power supply is sufficient for your hardware configuration, and lastly may be worth a clean remove/install of drivers.

They may still have some active threads at the AMD forums about the DX9 issues---perhaps there is a driver version posted there that will help.