2008 Chevrolet Malibu 2.4L Ecotec with OBD II Codes P0016, P0340, and P0341 - Diagnosis and Solutions

I recently purchased a 2008 Chevrolet Malibu 2.4L Ecotec with approximately 129,000 miles and limited maintenance history. The vehicle has been running smoothly until recently, when the check engine light activated shortly after an oil change at a commercial 'quick change' service. While I don't have extensive ownership time to draw definitive conclusions, the symptoms are concerning. The car starts reliably in both cold and warm conditions but occasionally stumbles or stalls at idle—sometimes recoverable by briefly pressing the accelerator pedal. Acceleration is generally adequate but can feel sluggish under load. OBD II diagnostics reveal persistent codes: P0016 (Cam/Crankshaft Position Correlation), P0340 (Cylinder 1 Cam Position Sensor Circuit Malfunction), and P0341 (Cam Position Sensor Circuit Malfunction), all currently active. Additionally, P0300 (Random Misfire) and P0506 (Exhaust Pressure Too High) appear intermittently. I performed a visual inspection of both cam position sensor connectors and swapped the sensors between engine banks to test for faulty wiring or component failure. I also inspected and cleaned the VVT solenoid connectors (intake and exhaust), applying lubricant to the valve portions, though resistance readings remained consistent at approximately 10 ohms. After draining and replacing the engine oil with 5 quarts of Mobile 1 5W-30 synthetic oil, the codes persist. I understand that P0016 typically indicates a timing chain or cam/crank correlation issue, while P0340 and P0341 point to potential problems with the Cam Position Sensor (CPS). I expected to see a code shift when swapping sensor locations—this did not occur, which raises concerns about either sensor integrity or wiring. While timing chain tensioner or guide wear is a known issue in this engine platform, such failures usually present more consistent performance degradation rather than intermittent stalling. A faulty crankshaft position sensor would typically prevent the vehicle from starting entirely—a scenario I have not observed. Given that the car runs fine most of the time, I'm wondering if there's another underlying cause or if a professional diagnostic tool is necessary to interpret these codes accurately. Could I be overlooking something? Is it time to consult a qualified mechanic with advanced OBD II scanning and diagnostic capabilities? Any insights would be greatly appreciated.