heating on the freeway is nothing to do with the fan , if it will cool in traffic the system is generally good , the fans running on the freeway could actually be blocking air flow or you have timing issues or the carb is lean or you have the vacuum advance connected to manifold instead of ported vacuum . the lower rad hose can be a problem also , you can bend up a wire coat hanger to go inside the hose keep the hose from collapsing , I would usea 180 * T stat & get a good quality Stant one