When the car was idling in the garage this morning (hooked up to HP Tuners), I saw a spike on the "Spark" graph at the same time as the car stumbled. "Control Module Voltage" also went from > 14 down to 13.69. Not a massive difference, but I don't know what the operating range for the computer is, so I can't tell if that's a real problem. It's weird that voltage would drop, though.
RPM also dropped from 850 down to about 740, then came back up.
It did this twice more over the course of about 10 minutes.