Maybe 10 degrees. I don't think that is the reason, though. When the truck was overheating in the driveway, it did it when temps were in the 70s as well as the 90s. It's currently 77 right now.
And when I say it didn't even hint at going over 180, I mean it didn't go to 185, 181 or anything else that would be deemed acceptable range.
This is how it always used to run regardless of outside temps. That includes 98 degrees on the downtown connector during stop and go rush hour traffic.