said by jcondon8:
Anyway this doesn't sound like the OPs issue anyway.
The page is imprecise in the sense that it doesn't explicitly state that traffic to these ports must be working for OUTBOUND connections to the Internet, and NOT inbound forwarded ports - the fact that the page mentions router port forwarding makes this even worse, so yes: no kudos to Microsoft for this one, the page sucks.
XBL wouldn't work in probably 98% of all cases if XBOX-Live truly required direct INBOUND access to ports 53 and 80 to the XBOX itself. Not a network administrator (the one at school/work they mention on the page in such scholarly, pass-the-blame manner) in the world is going to make that happen, the majority of all end-user devices in the world are behind NAT, or even behind double-NAT (that's a particular troublesome scenario for XBOX).
The OP has stated multiple times that he has bypassed his router by hooking up his XBOX directly to the cable modem - so none of the router-centric discussions here are relevant, and all speculation about them should stop.
OP: you'll need more information, and nothing is easy from this point forward: the only way is to sniff the traffic between your XBOX and the rest of the network. Hook up a legacy ethernet hub (hard to find, even borrow these days) between your XBOX and the rest of the network (home router, or if bypassed, the cable modem), and put a PC/laptop with Wireshark on one of the other ports.
Record traffic. Analyze where the majority of the traffic is going (XBL gaming server? PS3 traffic is very much peer-to-peer) , and whether that traffic dies (becomes one-way, with your XBOX sending, but not getting anything back, or only getting traffic back with delays) when you experience your latency issues.
Post the XBL gaming server IPs here, if you will, so other people can take a look how much latency or reachability issues exist with them.