What happens when you have an outage? No internet access at all from all machines? Are you able to access everything else within your network? Do you have a IPS in place? While you are having an outage are you able to bypass your network device and test your outbound connection? When you contact Comcast during an outage are they able to communicate with your router?
Once you get your issue worked out you might want to look into docsis 3.0 here is a link telling you about the benefits. I am running it at and noticed a significant improvement!