I did the same approach regarding the router. UPNP feature isn't available on AT&T Uverse routers. It is not going to be a router problem as the other 360 works consistently on various ports. I will note that this malfunctioning 360 would not scan (and display) games stored on the hdd when I first received it. That problem went away after I did a hdd swap. This occurred even when I had put it in the content/0000000000000000 folder.