Waterless Coolant

chasb said
So fan size might be the problem??

Your cooling system is capable of cooling the car, as indicated by the highway temps.

At low speeds (below about 35 mph) the cooling system is relying on the fan for airflow. Over that speed, you don't even need a fan.

So my best guess is that your fan is not capable of moving enough air or the air it is moving is not correct directed through the radiator.