I have noticed that the card goes into energy save mode and clocks down when loading track. Then it does not clock up to full speed when you enter track and get 17-18 FPS. Alt-Tab in out and it "wakes up" and FPS Is normal again, and sometimes it goes into energy save mode during race dropping to 18 FSP. In Nvidia control panel manage 3D settings, power management mode to "Prefer maximum performance" fixes this.
nvidia inspector Try this soft called nvidia inspector, you've got a parameter "power management" that you must set to prefer maximum power