You have a TATA segment that is getting a bit flakey:

7 42 ms 39 ms 71 ms if-22-2.tcore2.CT8-Chicago.as6453.net [64.86.79.1]

Notice the wide range for the responses---from 39ms to 71ms, just over an 80% increase in delay just a few seconds apart.

I would hazard a guess that under really heavy congestion, you start to see even more erratic responses on their segments (as6453.net). These are not under Comcast or SE's control, but are a routing partner that Comcast has agreements with for routing you through that corridor. So your ISP will likely be your best advocate in resolving this particular problem.

Might want to try running a pathping to gather a little more useful data for them to analyze what may be going on in your routing. It may take 7-10 minutes to run, depending on varying factors, but will provide a much better view of what is going on than just tracert (pathping hits each hop 100 times, and tries to collect data on hops between routers as well, not just pings from you to each hop). It would be best to run it when you are experiencing a lot of issues with your line for the best chance to catch clues on where the traffic is having trouble.