Or have the fan outside the radiator PUSH the air through the radiator and into the engine compartment.

The natural flow of air hitting the front of the vehicle as it moves forward is to pass through the radiator and into the engine compartment. If you are trying to pull the air forward through the radiator, it is meeting the air that is naturally flowing in the other direction. The result is the radiator is probably not seeing any or almost no air flow as the vehicle moves forward. Its a wonder it stayed that cool for that long! Gene