Do you have a fan clutch and if so have you checked to make sure it is engaging? A failing fan clutch can produce those kind of symptoms. If it is bad and you don't want to replace it on the road it might be possible to use some jumper wires and hot wire the electric fan to run constantly until you get home.
By the way, did you check to make sure the electric fan was engaging before resorting to the heater to cool it down?