Yup, we're on the same page.
I think I figured it out. My original theory was that the exhaust leak was causing excessive noise (not enough for the ECM to think it's a knock, but enough to raise the average KS voltage). The high average KS voltage then drops below the threshold required to set a P0327 after driving for a bit and coming back down to idle (exhaust leak makes far less noise at idle than at higher RPM).
I'd already listened to everyone who said there was no way the exhaust leak was the problem, and replaced both KS's and harness to no avail. After sealing up the exhaust though, I threw the code one more time on the first drive (expected, as the noise and thus average voltage would be low until the ECM figured out the new average). But it's been a week since fixing the leak and no more code.