[f16n]

I have a Shell Valley Cobra with a 427 fe,I have a heating problem at high speed.When I travel on highway for a distance temp. begins to climb 210 or more degrees,When I stop at light temp falls down to 195 or so,changed water pump from eletric to manual,changed thermostats,adjusted timing.Think radiator capacity to small,radiator holds 5 quarts water alone,looking at double pass raditor, Any suggestions please,Thanks Toren