Great post OP and I completely agree. Piece by piece the game is slowing down for him and we really saw it yesterday. Add to this the fact that he didn't throw one ball that was remotely close to being an INT. Just great decision making all day. Stepped up after the game got tied. To me, this was more convincing than his Tampa Bay game.
I think Nagy has also picked up a pattern for Mitch, and that is to get him relaxed early. Call some runs plays, easier passes, etc. Mitch tends to play with momentum, both good and bad. So I think we are going to see slower starts for him early with more conservative play calling early and then opening things up a little later in the game. Our inconsistency in pass protection is likely a part of this as well, waiting for the opposing D-line to get a little winded before calling the longer drops.