1997 Chevrolet 1500 5.7L V8 with OBD-II Code P0301: Diagnosis and Repair After Catalytic Converter Replacement

I own a 1997 Chevrolet 1500 equipped with a 5.7L V8 engine. Twelve months ago, I encountered a persistent P0301 diagnostic trouble code (DTC), indicating a misfire in cylinder 1. I performed the following repairs: 1. Completed a full tune-up using A/C Delco parts. 2. Replaced the spider injector assembly. 3. Discovered that Cylinder 1 had no compression; I removed the cylinder head and replaced both the bent and burned exhaust valve, along with all stem seals. For several weeks afterward, the truck ran smoothly and passed emissions testing. However, shortly after, the check engine light reappeared—this time without flashing. A scan of the Powertrain Control Module (PCM) revealed a catalytic converter issue. The vehicle continued to run well, so I cleared the code and replaced the downstream oxygen sensor for Bank 1. After driving approximately 15 miles, the check engine light returned. I recently replaced both catalytic converters with original GM parts. After driving about five miles, the truck ran slightly smoother but the P0301 code reappeared and the check engine light is now back on again. Any insight into why this misfire persists despite these repairs would be greatly appreciated.