[Sephiroth]

If that's what you're getting in the middle of the day, I imagine it's rather lower in the evenings. Cable Broadband should deliver full speed unless there is a circuit impairment or congestion.

The TV frequencies are different from (and thus don't clash with) the broadband frequencies. They all come down the same cable that goes to you external wall box.

If your Tivo coax cable hasn't loosened at either end, and if there is no line impairment, then at peak times it would seem that there is indeed congestion - though that is a rare occurrence going by what I see on the forums. A search on the term "pixellation" might provide more insight for you.