It's all good. I woke up at 6, and the probe was reading 175. I wrapped and let it go another 2 hours -- maybe a tad too long. But I just had a nice smokey breakfast. Brisket and coffee. Mmmmm, good.
(The brisket was 16 lbs, pre-trimmed. I stuck the probe in a tomato from the fridge, and it registered 36*, so I figured it was working.)