Please PM me your cable modem's MAC address (listed on the modem) and your current public IP (»
whatismyip.com) and I will look into this for you.
It would also be very helpful if you downloaded and installed PingPlotter Pro (free trial) and keep it running to a site/server you are able to replicate the problem to. After you see the problem show up in PP, you can then click "file, save sample set" and attach it to this thread.