Incidentally I love comcast. 150mbps cable, cheap price, no outages, free hbo, X1 remote rocks. Pricing is a bit annoying (paying extra for HD) but is a great product. Just thought I'd mention it because it gets too much hate.
As much as I dislike Comcast, I voted you up because I once also had this magic serenity for a few years.
Then I switched to Comcast for TV and it all went down the tubes. Random outages (sometimes daily), substandard speeds, Netflix speeds suffering (or stuttering) at peak times, etc.
Who knows whether this just reversion to the mean, or the techs botching the install. Even "reddit trick to email the Comcast VP" didn't fix it (though that did get a quick response).
I'm guessing you have FiOS and/or at least one other wireline broadband provider in your area.
Comcast is ludicrously expensive in my neighborhood where they are the sole broadband option. It's so bad the city council is looking seriously at muni fiber.