Xbox Live Connection Problems?

Alright, so I have this problem when i play a game over xbox live (Black Ops), I start a match with a 4 bar connection, but about 2 min into the match I suffer through severe lag and the "connection interrupted" on-screen text. Then I get booted from the match saying that I couldnt connect to the host. And occasionally, I am kicked of of xbox live entirely. My connection is setup through internet connection sharing, my laptop recieves the wireless network, and i share that connection to my xbox via ethernet. I recently reinstalled Windows 7 and this problem arose. I have never had a problem like this before. I have tried disabling my firewall, changing my NAT, DMZ, and port forwarding. All with no success. QoS is the other process i am looking into, however, i have no clue how to use it. My router/modem combo is Actiontec GT704-WG-B. Thanks in advance