Make sure your ATV is updated to version 5.1.1. There were some networking issues in 5.0.1. If it is already updated then switch to a wired network. Trying to do streaming video over WiFi rarely works well, even when using the really high end WiFi routers that are meant for it.
If it is still happening I would try doing a factory reset on your router. (You will have to re-do it's configuration and passwords if you do this.) And if it is still happening I would contact your Internet service provider to see if they throttle or limit bandwidth usage. Some ISP's limit the amount of bandwidth you are allowed to use or limit traffice from services like Hulu, Netflix and iCloud.