P0306 Fault in Cylinder 6 - 2004 Toyota 4Runner Diagnosis and Repair

I own a 2004 Toyota 4Runner that is currently displaying a P0306 diagnostic trouble code, indicating a misfire in cylinder #6. I took the vehicle to the dealership, where they replaced the spark coil packs from cylinders 4 to 6, hoping to isolate a faulty component on cylinder #6. After this repair, the code returned. I have since completed a full maintenance service, including replacement of all spark plugs, but the issue persists. The misfire continues to trigger the P0306 code despite these efforts. Any additional insights or troubleshooting steps for this specific fault in a 2004 Toyota 4Runner would be greatly appreciated.