I know this isn’t a “solution”, but ever since sending my original SB3 15 inch in for a replacement, the replacement has worked fine - no gpu drops. For now though, I’ve mostly kept away from any of the firmware updates and things seem to be fine for now (plus I can’t really automatically update the device since there seems to be some bug on my installation).
Side question - does anyone know why a windows installation on my SB3 might get stuck on checking for updates in settings? This has persisted through in place upgrades and updates through the update tool.