Random Frame Lag

[Zatoh.5627]

I need help. Ever since the recent Wintersday update, I've been getting a lot of sudden frame lag in my game. It usually runs at 60 FPS, but often it just starts to go straight down to 30 FPS and then back to 60 FPS after a few seconds. This happens even in non-populated areas. It has become really annoying, and changing graphical settings to improve performance doesn't seem to do anything to fix it. I even tried turning off the new motion blur feature since the frame lag often happens when I'm moving, but that doesn't work. Updating my GPU driver doesn't appear to change anything either. This problem has only been happening in Guild Wars 2, and none of the other games I play. Is this a cache problem? Do I need to reinstall the game? Or is this a problem outside of my control?