I have already replaced my thermostat, new radiator, fan works, top hose gets very hot and water pump is working fine. When I drive on the hwy and take the rpm's over 5000 my temp slowly rises to hot. If i come to a light it will quickly return to a normal temp, however as soon as I take off it goes right back to hot. I can help keep it a little below hot if I keep the rpms low when in 5th. I am thinkin its the Head Gasket but this is a new one for me... Any ideas would help get me started?