1998 Chevy Camaro engine is starting to run hot

1998 Chevy Camaro mileage: 70,000. Everything is stock, and it has 70,000 miles on it. The engine is starting to run hot, at 250 degrees. Even at nighttime, it runs hot. I have replaced the radiator, electric fan motor, hoses, thermostat, but it still overheats. Someone told me it might be the catalytic converter is clogged and needs to be replaced. Is this true? How do I check that?