My vehicle jerks and stalls while driving, usually when I speed it up. I've already chan the gas filter, the catalytic converter, the gas regulator, spark plugs, wiring and coils. Even though the jerking problem is not as worse as it used to be, the car still stalls. Can anyone help me please?

Before it was parked it was spitting silver looking pieces out of the tail pipe. Catalytic converters are cut off and straight piped. Now it won't start, has been sitting. New battery, plugs, wires, coils. Idk.