I am getting normal response from most sites, but a few that always worked in the past never load. Some examples:
www.vrbo,com
When I switch my connection, using the same browser, to my mobile phone tethered, these sites load normally.
I tried NSLOOKUP on the sites, and tried to manually load the resultant IP's, with no change in result.
I disabled firewalls in my router, and tried multiple browsers on multiple computers. The only thing that made a difference was using the tethered mobile connection in place of comcast.