If you removed the thermostat for troubleshooting purposes would you be able to rule it out as a culprit ? You coud take the thermosat and put it in a pan of water then heat it up and then verify when it physically opens with a thermometer . I also have seen high temps at highspeeds caused by a bad lower radiator hose,the springs were damaged and allowed the lower hose to collapse and waterflow was restricted to the water pump (lots of money and parts were replaced instead of a 5 dollar hose).good luck,Johnny

__________________
85 300sd SOLD ,85 745i,95 740i,1972 Suburban,1938 International