2005 BMW 525I Engine Problems

I am encountering persistent issues with my 2005 BMW 525i. Despite having replaced several critical components, including the ignition coils, spark plugs, mass air flow sensor, and throttle body sensors, the vehicle continues to experience performance problems, specifically failing to advance beyond the fourth cylinder when driving uphill. After conducting numerous diagnostic tests, I have concluded that there may be an air leak in the intake manifold. Additionally, after prolonged use under these conditions, the positive battery cable from the trunk has shown signs of overheating, evidenced by smoke, which I suspect is related to repeated uphill driving. While the vehicle performs adequately on flat surfaces, it exhibits hesitation and jerking once it surpasses the fourth cylinder.