It's probably not even the thermostat. A bunch of people with the 2017 Acadia Denali have experienced that same exact symptoms as have I. It seems that if you unplug the Negative Battery Terminal that it clears these errors and everything starts working normally again. It worked for me.
I almost dropped $1400 to have the thermostat replaced. Then I did the battery terminal thing and cleared the errors. If it was the thermostat like I thought then the issue would have came right back as I have been driving it all over town and it's been in the 90s here in Arizona already. Been a week now and everything is working fine.
I think this is just another software gremlin with the 2017 Denali.
Interesting, I literally just got our 2019 back from the dealership (Friday) for having them replace the sensor. Thought it was good to go until I started driving home this afternoon and got the steering is reduced and realized the gauge isnt moving again. I am going to have my husband try your battery idea and see if it works. Not sure I want to go pay to have the thermostat done - when the gauge works its fine, hence why I thought it was just a sensor issue.