Again, I have a D3 modem already. The night time slowdowns happen every night and its just not only the bandwidth that slows down, it's also sometimes connecting to sites, packet loss, and pinging servers take 200ms rather than 30ms for example.
I guess the only thing I can do is call comcast and complain?
Or you could post some evidence of all of that while it's happening.
I've seen cases like this where it was someone else on the customers wifi network causing these issues while he was home from work at night. -- Ex-Tech at the Beach. I speak for myself, not my former employer.