Overheating while traveling and got a check engine light

I have a 2001 Camry LE 4cy with ~133k miles. On the way from South Carolina to VA, the engine began to over-heat and the check engine light came on. Monitored until got to our destination. The temp gauge kept going up and back to middle. Went to Toyota in VA next day to check codes. The over-flow tank was full and venting under the hood. They said it was a bad EGR valve and catalytic converter. Had replaced ($1300). Not know any car repair people in VA. On way back to SC, started over-heating again. Stopped every 30-40 miles to add coolant. Reservoir was full and still venting. On the way, I thought it might be the radiator cap since coolant was going into the overflow. We were traveling on New Year's Eve, so nothing was open. Got home and took to my mechanic. Performed leak and pressure tests-everything fine. Said thermostat was working since I had heat and coolant was rising and falling in radiator. I have since noticed that when I stop at a traffic light, the heat gets cold. Thanks for your indulgence on this lengthly question!