if you are suddenly "stuttering" it may be because u have vertical sync enabled. that makes the graphics card put out what the monitor is meant for (likely 60hz, so 60 fps) but if the card dips below much of that, it will stutter and drop to a multiple of 60 (30, 15, etc). try turning v-sync off. this will also probably result in screen tearing depending on your monitor's refresh rate. but it will produced smoother movement and less stutter.