It sounds like your fan has a built in shroud. If so, try taking the fan off the car and run it on the road and see if the temps drop while at speed. If so, you might try one the the fans without a shroud, it would let more air flow through the radiator. The speedway fan I have has a built in shroud with flaps in it. Place the fan on the lower part of the radiator if you have room to move it down.