2002 Grand Am 3.4L P0404 and P0300 Codes: Surging, Sputtering, and Random Misfires - Diagnosis and Solutions

I'm experiencing persistent drivability issues with my 2002 Grand Am 3.4L engine, specifically surging, sputtering under acceleration, and a complete lack of power when climbing hills—like the car is fighting itself. The driving experience feels unstable, as if there's fine china under the gas pedal. I've already performed several common fixes based on prior experiences in the industry: replaced the fuel filter (backflow looked like mud), spark plugs, ignition wires, air filter, and fuel pressure regulator—all of which were due for replacement anyway. I also changed the transmission fluid and filter. However, these repairs only seemed to worsen the symptoms. Eventually, the vehicle began setting two diagnostic trouble codes: P0404 (Exhaust Gas Recirculation System Flow Malfunction) and P0300 (Random/Multiple Cylinder Misfire). After replacing the EGR valve, the P0404 code cleared—but returned within 15 miles, along with the P0300. When I unplugged the new EGR valve, the symptoms improved significantly—surging and sputtering were reduced, though still present. Exhaust flow appears normal; no rattling from the catalytic converter, and no vacuum leaks detected. Wiring checks also came back clean. I'm now wondering whether the issue lies with the PCM (Powertrain Control Module) or if there's another underlying cause—such as a faulty EGR position sensor or incorrect EGR valve operation. I’m specifically looking for guidance on: - What voltage should be expected at the EGR harness? - How does the PCM determine when to send signals to the EGR valve? - Are there known issues with 2002 Grand Am 3.4L engines related to EGR port clogging or EGR position sensor calibration? Any insights, especially from owners of similar models or those who have resolved this issue, would be greatly appreciated.