Well... got the car back today. Dealer did the work under warranty (I had back in the collision shop to fix a few things I wasn't happy with) and indicated it was a loose ground connection on the engine block (or header.. don't recall now sorry).
Anyway.. drove it home tonight without an issue. I'm heading to Ohio for the twisty run this weekend... so we'll find out if it's all good now after the long drives this weekend.