Nostalrius Begins - Quality wow vanilla realm (1.12)

I was leveling with smooth performance in STV for a couple hours today, when out of no where the game started to perform like a power point presentation. After running around, STV definitely seemed overpopulated, and I know the entire server is overpopulated, but this zone seemed especially overrun. Anyways, I ran into darkshire and my game immediately went back to performing smoothly. Ran back into STV and the stuttering started up again. I'm assuming this issue has to do with population. I had other players in STV at the time test the frame-rate issue by going into darkshire and they experienced the same. Also this isn't minor stuttering, it's unplayable.