I have a 1990 chevy lumina 2.5 L 4 cyl. 100,000 miles....The car recently started chugging while in drive and will not accelerate correctly, when I do get it to 55 mph theres still chugging, Ive replaced the fuel filter, spark plug and wires, fuel system clean, new battery, there is a inch crack in the exaust manifold on the front of the engine, not sure if that would make me lose power to accelerate, the car idles fine, but chugs when put in drive, and will occasionally die when put in reverse....PLEASE HELP