My M.C. was overheating at stop lights. Called radiator shop and he gave me good advice. He said if it gets hot at the light, but cools off going down the road, you have a bad clutch on the fan. The usual test is to spin it and if it stops you think it is OK. It is not. He told me to pull it and if there is oil on the front of the clutch it is bad. It was. A new one made all the difference, and you could tell it with the hood open. I like the fan clutch over a flex fan, as I had to make a decision and chose to go with GM's design and it works.
Plus a chance to clean up the fan and paint it, which I had not done.