Well, myself as well as many other people are stuck with their NAT settings set to STRICT. Unfortunately, this makes your online play, depending on the game, a little sucky. So, I tried to find out, and I did. This might not be the nail in the coffin to your internet issues, but it worked for me.
So, you first have to find your Admin Panel for your router/gateway (usually accessed by typing the IP address in the addressbar of your internet browser). Then you have to get into the advanced settings and configure something called the UPnP (Universal Plug'n'Play). This normally is set to be DISABLED, but that's not what you want. Go in andENABLE it, but don'tscrew around with anything else, and it might screw up your wireless internet. Then you should save the settings to the router/gateway, and restart both your router/gateway, and your XBOX360. When you run the test again, it should read as OPEN, and you should have no more problems with XBOX Live.
PM me if you have any questions, or if you just need more details.