2000 Pontiac Bonneville EGR code issues

Engine Cooling problem
2000 Pontiac Bonneville 6 cyl Automatic 141000 miles

I have a 2000 pontiac bonneville SSEI. About 4 weeks ago it went to the dealership to have the harmonic balancer replaced. The car ran fine after that, except a minor humming noise that seem to come from the area of the belts. About 2 weeks ago I went and filled my car up with gas at Walmart, drove about 10 or 15 miles and the check engine light came on. I have the service engine light code was P0401 for the EGR valve. I replaced the EGR valve, my car ran fine. A few days later I filled up with gas again, drove a few miles, the service engine light came back on. I had the O2 sensor and spark plugs changed. Car seemed to run better and light went out again for a few miles. Now my engine is overheating, after only about 10 minutes of running time and my catalytic converter did glow red once, before I changed the spark plugs and O2 sensor, but not after that, that I could tell. My EGR valve is fine what is making the service engine light come on and give the P0401 and P405 codes and why is the engine heating up so fast. The cooling fans work, in fact, they come on minutes after I start the car, even at idle. I want to know what could be the problem. I keep going in circles. One other thing I noticed after all of this is a slight whistling noise near the belts. Please help!