I've found that if you use the trainer during career mode it can possibly corrupt the data, and the mission markers will not work. If you have problems like that, just reinstall the game or just use it on another user account.
Make sure that your PC meets the system requirements, if it does not just upgrade it. I remember I had a less bad version of the problem, and it was due to ly Low Quality graphics card.
To save the visual settings hit enter and then space I think.
If it really bothers you I would say just reinstall the game. Changing the handling should usually do it though. If you backed your files up, you might want to try and put it back to normal, but this will replace all of your car mods...
The lightbar looks great. The traffic advisor is a nice touch. The original Crown Vic templates don't fit the Driver Sf version good, Oh and by the way I've got an LAPD style push- bar available in various formats, tell me if you are interested...
I suggest that you check your keyboard. I have a similar problem when I first got Lcpdfr. Try another keyboard. Your PC specs seem to be good, so that is probably not the problem. You might also have to reinstall the game, and just start over.