I am not saying this is or will fix anyone's problems or issues.... But,
In the colder months the engines heat can not burn out the condensation properly in the Throttle Body... So therefor you may get a rough running motor or a message that says "reduced engine power" Over the last 3 months I have seen at least 20 of these at the shop Including my daughters car that lost power on the highway. The process to Clean the Throttle body is Very easy and can be done by anyone with a simple hand tools, a wire brush and GM "top engine cleaner" I have my Vehicles done twice a year along with the injection induction clean.
I work at a GM dealership and am close friends with all the techs at my store... When they tell me something I trust them... Am I saying all dealership techs are this way? No... But you may have to trust them sometimes.