It's my bosses truck, 98 ECSB, 4x4 5.7. Some shop has changed the plugs, wires, cap, rotor, crank sensor, ignition modular, but it's still throwing misfire codes. He says on some days it runs fine, but engine light will flash, and other days it will buck and run like crap in the lower RPMs. What could be wrong?

Thanks.

 

change the distributor its self

 

Ignition coil, vacuum leak, fuel pump?