[pjsg]

I had a problem with Comcast that was that native IPv6 traffic was slower than IPv6 over my Hurricane Electric IPv6 tunnel. Support was no use (no surprise). But I happened to meet someone who worked in Comcast's backbone network. He figured it out and I got 10ms knocked of my native IPv6 ping times. (See https://n1dq.blogspot.com/2015/03/ipv6-comparing-hurricane-e... for the story).

The moral of the story is to find someone who works at Comcast who has Engineer in their job title and reach out directly. Linkedin is your friend here.