2000 Buick Century stumbling

While driving at a moderate speed, does it matter if it is 40, 50, 60, or 70 miles per hour, car suddenly starts to stumble on and off, almost feels like misfire in spark, plugs or wires. I have replaced all of them and it still does the stumbling. Replaced coils and control module, replaced gas filter, checked for vaccum leaks, none noted. Also, no codes.

Unplugged electronic EGR value, car runs perfect at all times thereafter. Bought a new EGR value to replace old one. Car is back to same problem. Can you help, ready to set car on fire.

Thanks,

Rick