1997 Mitsubishi Eclipse radiator

Did you replace the radiator because it was leaking or because the overheating problem? You should have start with the simplest and the least expensive items first, which would have been the thermostat, and then the engine coolant temp sensor.

Do happen to see the coolant reservoir boiling as soon as the engine is turned off? You may also want to replace your radiator cap, just for a good measure.