Do you use the cheezy thermocouple probe with the fan controller? I have the same fan and I think the probe is to blame for improper cooling. Since the probe is supposed to be in a part of the radiator that doesn't see airflow from the fan, I think it may be affected when it sees airflow from the vehicle moving, making the probe think the engine is cooler than what it really is. My car seems to run hotter in the cold months, and I think it has to do with the ambient air temperature affecting the probe's reading. Seems like you should have enough airflow on the highway that the fan wouldn't need to work much anyway, so I don't know how my theory holds up in that situation.