Here is how I fix the problem.
At game main screen,Click on "Options" then click on "Video" next click on "Advanced" and then look for the setting control call "Foliage" and slice this setting all the way to the LEFT.This is very importance that no matter what other control bar that you set, this "Foliage" setting has to be all the way to the left at all the time. Hope this will help someone out there with the same problem.
Thank you tp1234! I did as you said and turned of foliage. The game no longer stutters.