Hey Clois:
No matter what %
antifreeze you use, or which fan you have, or which radiator you have no car should overheat at 45 MPH in high gear.
Make sure the coolant is flowing through the radiator at sufficient volume. It could be that your water pump is just sending most of the coolant through the heater core and not the radiator. The coolant will take the path of least resistance.
Bob