Xbox live multiplayer issues, ATT internet 300, Gateway BGW210

I am having recurrent issues connecting to multiplayer games with friends via xbox live. I have ruled out microsoft for being the issue. It is purely an ATT internet issue. I have opened my NAT type through IP Passthrough and only worked for a few hours (3-4 days at most) before I would again disconnect from my friends. Either it would switch back to a strict/moderate NAT type or it would disconnect for an unknown reason. I have reset my gateway, reset my xbox with no success. I need a permanent fix for this issue or I will be forced to switch providers as I have never had this issue with any other internet service. Should I get a router to put in between the gateway and xbox? Give me something useful, I do not need a link to an article showing me how to open my NAT type.