Interesting....I m having the same problem as in if i drive slow it heats back up and on freeway it will cool down...I just assumed that the Thermostat was just busted but if yours still active like that its really odd.....ill be changing mine soon but ive read that if you change that its time to change the water pump also...and im a little tied down with money so maybe next month...but ill post how mine goes once i do it.