[thstone]

Sounds like one of the radiator fans isn't working at low speed. Easy way to check: Start car cold, turn on A/C, both radiator fans should come on at low speed. (You can also use a Durametric to manually turn on both fans from the engine controller section). If one of the fans doesn't turn on, then its either the fan relay (rare) or the ballast resistor (most common) for that side fan.