Came home just in time for the Comcast tech to show up. First thing he did was replace the line coming in from the pole. He also replaced the modem (again), just to be extra sure. So far, no problems. No recurrence of sawtooth pingtimes. Worst I've seen so far were a few single spikes of ~1s. For the past 6 hours, our average ping is 77ms. I've managed to catch up on half of my hulu queue already.
Need to go to the pharm tomorrow and get more doxepin. I ordered a refill, but it's too soon for the insurance to pay for it, but the stuff is cheap.