More data: running on jackstands again, I notice that the vibration seems to come and go, one second on, one second off with speedometer reading 40 mph. Also, it might be more pronounced during coasting than acceleration, though I can't say for sure. Is this a problem in the differential gears?
I did swap on a different wheel on the right side, and the wobble is now more up/down, less side-to-side. Tire shop said the wheels were straight, but I'm not so sure.
