For some reason, whenever i go outside, the fps drops to 30. it acts like it wants to go higher but it'll hover around 29.5-30.5 and it rarely drops below. But in a house or some other interior, i can get 60+ fps. Any ideas?

Also, the gpu isn't a problem. I've got a gtx 260.
the cpu is a problem but only when im around npcs and i'm usually not around any in the wilderness.