P1151 and P1152 Fault Codes on 1995 Ford Windstar 3.8L Engine - Diagnosis and Solutions

I own a 1995 Ford Windstar with a 3.8L engine, currently at 145,000 miles. The vehicle was serviced under warranty when the engine was replaced at 82,000 miles. I am now experiencing poor acceleration during slow starts—when accelerating from a stop, the response is sluggish. However, if I accelerate quickly or reach highway speeds (around 45-50 mph), the engine performs much better with smoother acceleration and less hesitation. The engine idles smoothly at startup but becomes rough as it warms up. Once cruising at 1500–2000 RPMs on the highway, the vehicle accelerates more efficiently—until suddenly, it begins to hesitate and stumble again during acceleration. I have already replaced several key components including the EGR valve, IAC valve, PCV valve, throttle position sensor (TPS), coil pack, and all four oxygen sensors (last serviced at 130,000 miles). The MAF sensor was cleaned extensively, removing significant carbon buildup. A K&N air filter is currently installed, and I do not over-oil the engine as some recommend. The spark plugs—Bosch +4 type—were replaced in June at approximately 12,000 miles, along with ignition wires. The vehicle occasionally backfires during acceleration from a stoplight. I suspect a clogged catalytic converter, especially since a previous inspection reported a rattling sound originating from the exhaust system. I have also checked all vacuum lines for leaks or cracks. Any insights into diagnosing or resolving these issues—particularly related to fault codes P1151 and P1152—would be greatly appreciated. Best regards, Justin