If I'm not mistaken, I think that type of stutter occurs due to loading a lot of textures. Since you've indicated that you have almost 1gb of vram available, I would think that it isn't related to your GPU as much, but rather the speed of your drive. Are you using an HDD or an SSD?This could also occur based on the current load of your GPU. I would look for the current usage of your GPU when it occurs to see if it is being fully utilized.EDIT: If your GPU isn't under 90%+ load when it occurs, I'd look at your drive being the bottleneck.