reduce engine power light wierd

I was hoping someone could help with a wierd problem on my 1999 camaro 3.8L. It runs fine at first but after it has been running for a while the (reduce engine pwr) and check engine light will come on and the car will stall out. If you leave the car off for about 5 mins it will start up and run fine for a while. And the check engine light as well as the reduce engine pwr light won't be on. Here is a list of all the parts i have changed Plugs/wires,air filter,fuel filter,pcv valve, downstream O2 sensor,catalytic converter, ingition control module(this did actually fix another problem). I am soo frusterated with this car i would really appreciate any imput. thanks