As it turned out the overheating was the result of three bad sending units. I finally borrowed a laser pyrometer and checked each cylinder wall, radiator, water pump,
oil pan, etc., each check out OK. Then I boiled some waster and put my thermostat in and checked when it opened and the reading of the gauge. I had bought these (last 2) gauges from the same source within days of each other. The gauges were fine except the sending units were mis-calibrated. I changed so many things that I may have had a problem caused by several things but all seems to be ok now. My gauges were reading almost 100 degrees hotter than the actual temp.