Definity get the radiator checked. They'd be able to tell if it's plugged up by checking the temp. across the radiator. I'd also check the condition of the hoses. I know of some cars that the hoses will collapse due to pressure and age and block off cooling systems. And like Jeff said, make sure it's full and that it was bled. Since whoever worked on your car seemed to now know what was going on, make sure the fan is kicking on. You can have the sensor changed once a day and if you have a wire problem it won't do any good.