Running Hot on the Highway

Just took it out and cruised it 65 mph on the highway and it got hot again so I pulled off into a gas station that was right off the road. Radiator and hoses were not hot at all but you could burn your fingers by touching the intake manifold under the thermostat and on the intake coolant passages coming from the heads right where the sending unit is located. But when I go onto the back roads it runs nice and cool. I think the thermostat lets coolant through but not at a fast enough rate. So I'll pick up a 180 degree and put that in there next. I am going to test it in boiling water before I put it in.