Hate to break this to you. I have the same issue. Just dropped it off at dealership. I had a regular shop look at it and they tested the coolant for exhaust gas. It was present. Therefore. There is a high likelihood of a head gasket leaking exhaust gas into the coolant.
There is a TSB for...
Sorry, I figured out that it was going to be a PITA to ship. We were driving to Gatlinburg soon, but that looks unlikely now. I’ll let you know if we make the trip.