After talking with Shaw support, they’ve decided that it’s probably best if they just replace my cable modem with a newer one. They can’t really say if it’s the specific cause of my problems, but it’s a Motorola CyberSurfr, a positively ancient model at this point, and they’ve been trying to get people off of them anyway. I’ve been using this one for over ten years now, and the tech was surprised I’d still had one for that long, since most people experience problems and swap it out long before that point.
So, tomorrow I say goodbye to my old friend as I drop him off downtown. It may be old, but it served me well for an awfully long time.