I had this problem for a really long time and had almost given up trying to fix it but this install of the game fixed the issue for me [
drive.google.com].
This install is in italian by default but editing the f1system notepad and changing language to English (or whatever language is preferable) fixes this. I'm not sure what is in this particular install that makes it work but it works perfectly for me.
Another thing I've learnt is for some reason using a shortcut for GPxPatch causes the game to start running badly again and I had to do a complete reinstall of the game to fix that so that may also be causing your issue.
Edited 1 time(s). Last edit at 10/07/2016 12:19AM by pironi14.