2000 Chevy S-10 P0172 Diagnosis: Random Hard Misfire in Warm Weather with No MAF Sensor

I own a 2000 Chevrolet S-10 LS Extreme with a 2.2L flex-fuel engine, 5-speed manual transmission, and over 140,000 miles. I'm experiencing a persistent and random hard misfire that triggers the P0172 code (Bank 1 - System Too Rich). The check engine light comes on intermittently and then turns off by itself—this happens regardless of whether the MIL is on or off. The misfiring becomes more noticeable in warm weather or during rain, and it only occurs after the engine reaches normal operating temperature (typically after driving for 30 minutes or longer). On colder days (below 45°F), the vehicle runs smoothly with no issues. I've already replaced multiple components including: - Spark plugs (twice) - Ignition wires (twice) - Coil pack - Valve cover gaskets (twice) - Throttle position sensor - Idle air control sensor - Crankshaft position sensor - Manifold absolute pressure (MAP) sensor - All vacuum lines I could locate - ECU - Fuel filter - Throttle body and throttle body gasket - Both oxygen sensors - Coolant temperature sensor - Ignition coil module - Fuel pump I've also cleaned the throttle body, inspected all wiring and connectors (all appear intact), and found no visible issues. At idle, RPMs remain steady around 80 or so. However, when driving uphill or cruising at higher speeds, misfiring occurs randomly—especially between 1,500 and 3,000 RPM. Notably, if I keep the engine above 3,000 RPM, the misfire typically stops. I've taken it to two different repair shops and once to the dealership—all diagnosed issues they claimed to fix—but the problem persists. There is no Mass Air Flow (MAF) sensor on this vehicle, so fuel delivery is likely being managed through other sensors or systems. Given that the P0172 code indicates a rich mixture in Bank 1, I'm now considering fuel injector failure as a potential root cause. Any insights or suggestions would be greatly appreciated.