|Well, first off, describe the problem you're having to the tech, just like you did to us. Also, make sure he sees your ping tests.|
Other than that, there's nothing we can do. Your LAN (local area network) seems to be working fine and so does your internet other than in-game.
If you're connecting your xbox via a wireless adapter, humor me and try connecting it via a network cable and then test and see if it still happens. Wireless is not very good for gaming.