2005 Ford Expedition 5.4L 3-Valve Engine Lean Code P0171 and Misfire P0305 - O2 Sensor Issues & Fix

My 2005 Ford Expedition with a 5.4L V8 engine is showing a lean fuel condition on Bank 2 (P0171) and a misfire on Cylinder 5 (P0300/P0305). I initially replaced all spark plugs, which improved the situation temporarily. However, after driving about 60 miles, the truck began losing power, experiencing slow acceleration, and backfiring in the intake manifold. The check engine light reappeared with a misfire detected on Cylinder 3 (P0303). After replacing the coil pack for Cylinder 3, the performance improved slightly. During my spark plug replacement, I noticed two previously installed coils that appeared to be low-quality and poorly made—so I replaced all three coil packs. The truck ran significantly better after this change. However, backfiring and popping in the intake persist. I cleared the codes again, and the engine runs smoother initially but begins to misbehave during acceleration—especially when going uphill or exceeding 60 mph. At times, it runs perfectly at idle and low speeds, then suddenly loses power and starts popping. The most recent scan revealed a lean condition on Bank 1 O2 Sensor 1 (P0171), shifting the issue from Bank 2 to Bank 1. I have replaced the Bank 1 O2 sensor with no improvement. The engine tends to run better after clearing codes but deteriorates under load. I'm now at a loss for what could be causing this persistent lean condition and misfire. Any insights or troubleshooting steps would be greatly appreciated.