Hmm. Would this fix my issue where my light comes on after 30 miles at freeway speed, even though all tires are in pressure spec (can restart car and get another 30 miles no problem)? Incredibly consistent, independent of outside temperatures.

Great!

Magneu sounds like you have a TPMS battery right at the edge of failing.

Would hope not, brand new TPMS when I got the wheels from TireRack. Guess I'll give them a call.

Before making the call I'd inspect the pickup sensor on the wheel hub but I can't think of any good reason why it would consistently fail from highway driving.

Where can I find said sensor on the wheel? I know they look vaguely like a drum key (a "T" with a really fat top), but I thought they are inside the tire?

I'm guessing it's a temperature related issue, as sustained 60mph+ is going to raise tire pressure one or two PSI. Apparently the sensor doesn't like that.

The valve stem is the top of the sensor and the rest is inside the wheel. It shouldn't be triggered by too much pressure though.

Seems easier to find the wire leading to the light and disable the light and just make sure to check your tire pressure

There isn't a specific wire, it's all on the car network CANBUS, the BCM reads the signal and turns the light on via CANBUS to the dash if it doesn't have the correct data