overheating!

This is outside of a fan problem. Have you changed from the red coolent yet? With the motor cool take off your radiator cap and look for gunk build up. The thermostat could be clogged up not letting it open or close all the way. I had a Chevy 305 that was missing the thermostat completely and it never got hot on the highway but was hurting in stop and go traffic. Coolent wasn't in the radiator long enough too cool down and coolent in the motor wasn't there long enough to absorb heat and pull it out of the motor. Make sure your sensor is working right and flush the coolent system and if that doesn't fix it, replace your thermostat. Almost forgot, the red coolent led to a massive recall due to it's corrosive attributes on intake manifolds and gaskets. Some vehicals may still be covered for repairs on this.