sounds like you have a low coolant problem.

Heres what to do:
WHen the car is COLD, pull the radiator cap. Fill the Radiator with WATER. Note how much fluid it takes. If its low, then you either have a leak or a blown headgasket. It means coolant is going SOMEWHERE, you are losing it somehow.

If the radiator is full of coolant, then you have a distribution (water pump) or flow problem.

Now, if the radiator is low on water, i would fill it up then start the car up wiht the cap off. Keep filling it and let the car get to operating temp and the thermostat should open. when the thermostat opens, fill the radiator to the top, put the cap on, and go drive it. Drive it for a few hours, or a day or two, then recheck the water level. If its low again, YOU HAVE A LEAK or BLOWN HEADGASKET.

If your radiator is not consuming or losing water, i would replace the thermostat first with an OEM TEMP Thermostat.

WHen was the last time you had a water pump put on?

usually overheating on the highway is a low coolant or water issue.

Its very hard to blow a honda headgasket so unless you have pegged H for a long time, thats prob not the issue. And stock radiators can handle 400whp no problem. SO if you are NA, you dont need a bigger radiator.