From my recollection just the engine controller.

My wife had a 2012 300 with the lower horse 3.6. Gave her great mileage (31/35) and was pretty quick with the 8 speed.
She got a great deal on a 2015 and traded in her ‘12. She wanted the sunroof, backup camera and all the additional stuff her ‘12 didn’t have.

She paid the price by getting worse mileage.

I did the research to see what might have changed.

All the engine parts are the same, cam, heads, etc. axle ratio same too. Same 8 speed.

Turns out the engine controller was different - more spark and fuel. Runs like a scaled chicken 🐓 but not happy with the mileage.