After maybe 10 mins of play, the game begins to stutter very badly. I looked at memory usage, and it's up to over 2gigs. Now I have 8gigs of RAM and a 64bit system, so there's no worry of running out, but still that's a really high usage after only a short amount of play. Is this the cause of the stuttering? How can I fix the stuttering, it's become unplayable when it starts to happen.