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Q:

missing on 1997 Chevrolet 1500 Pickup

Rookie cbe0621eac06868b3efe0d8d1d3611e23c60d3114864ea2ec19a68cfbd3eebab
eng idles fine under load it breaks up -missies changed fuel filter recenly mechanic put new fuel pump because truck would not start
(1) Answer
You could have ignition system troubles or fuel system problems. You need to get the ignition system checked (sparkplugs, wires, cap and rotor), including spark strength under load. You also need to check the fuel pressure when the engine is cruising and under load, which can be done by safely connecting a mechanical fuel pressure gauge to the test port on the injection system and go for a drive. Use adequate cautions for fuel pressure testing while driving.