This is the same routing problem that has been going on now for weeks.
Look at that mess in that ping plot.
From Fresno to
Sacremento to
Oakland to
Sacremento to
San Jose to
Chicago to
San Francisco to
Los Angeles to
Dallas
Like Max said, you need to get a hold of Comcast, and get passed the first level of support. Once you get to Tier two support, point them at this thread. If they cannot see what the problem is, get another ISP.
This problem has been ongoing for over a month now. One day it works fine, the next day it is exactly what you see Fianna. Almost as though someone, somewhere has stored a bad backup of the BGP tables and they keep reloading that bad copy. This is reaching levels of incompetence I cannot comprehend.