Yeah, only way around it is to force each pc/tablet/phone/tv to use the dns server for pihole and so far has been working but this setup I have lost my whole connection vpn protection I like to do for torrents and iptv streaming.you can't change your DNS on Comcast even with you're own gear. You put in your own DNS information, and it doesn't matter, as Comcast forces the DNS suffix on your connection no matter what. At least this is how it was when I tried to switch my DNS servers.
I have a docsis 3.1 modem I can see if they will activate so I can go back to my system setup. I really only wanted the XFI crap for the unlimited internet since doing that was $25 vs $50 on my old gigabit plan.