Russell,

You are alluding to the fact you don't think the gauge that reads HOT reflects actual engine temperature..correct!

A simple thermometer in the radiator filler neck will give you true water temperature which you can then compare to the gauge.

A new sending unit doesn't cost very much. If I were questioning it at all, I would start with the sending unit then see what happens.

This is assuming the system is full, purged and the thermostat is functioning properly.

Many radiator shops consider a 'cleaning' a reverse flush and paint job. If the tubes are partially plugged with mineral deposits, which are almost impossible to remove, then your radiator can't do its job properly and you will never triumph.

Stuart