2015 Chevy Spark P0301 Cylinder 1 Misfire: Diagnosis and Repair Help Needed

ERROR CODE: P0301 I own a 2015 Chevrolet Spark and have been experiencing a persistent cylinder 1 misfire indicated by the OBD2 fault code P0301. I've already attempted repairs at a local garage for over 15 days with no resolution. I've replaced the spark plug set, ignition coil, and all wiring harnesses. Fuel injectors were also tested and found to be functioning properly. In addition, I performed a full engine disassembly to inspect internal components such as pistons—no visible damage was detected. After reassembling the engine, the issue persists. I'm now extremely frustrated as I've spent significant money on repairs with no progress. Can anyone provide guidance or suggest further diagnostic steps? Is there a specific test I can perform at home or through a professional to identify the root cause of this misfire? Any insights or solutions would be greatly appreciated.