1997 Chevrolet 1500 4.3L Engine P0306, P0131, P0174 - Cold Starts Fine, Warm-Up Bogs at 35mph with Loss of Torque

I have a 1997 Chevrolet 1500 with a 4.3L V6 engine. The vehicle runs perfectly when cold, but as it warms up, it begins to bog down and will only reach about 35 mph at around 1500 RPM. After turning the engine off and restarting, it runs smoothly for approximately three miles before losing all torque—similar to a clogged catalytic converter. I've already replaced the MAF sensor, distributor, rotor, MAP sensor, spark plugs, ignition wires, and performed a cat cut with no improvement. The issue persists despite these repairs. I'm now at a loss as to what could be causing this behavior. Any advice or troubleshooting steps would be greatly appreciated. Fault codes P0306 (cylinder 6 misfire), P0131 (oxygen sensor bank 1, sensor 1 low signal), and P0174 (fuel trim bank 1 too rich) are present in the OBD-II system.