Hello I have a 1998 k3500 with a 7.4l 454 in it. It started over heating and I dropped it off at a local shop, found there was a crack in one of the tanks on the radiator, while they were replacing that I had them do a thermostat and plugs and wires. I went to pick it up and it was running like it had a misfire but through no codes I ran it like this for about 2 weeks while trying to diagnose the problem. Then running in my driveway it just decided to stall and would turn over but won’t fire. I figured it was spark related so I started chasing, at this point the plugs and wires were replaced again, the ignition coil and ICM, the whole distributor with a new pickup coil. It’s timed. It’s getting 55 pounds of fuel pressure to all 8 injectors, fuel pump is kicking on, has power to the ECM has ground and has ignition, the crank position sensor was replaced as well, I tested the spark with a spark tester and it’s getting good spark tested all my fuses checked all my grounds, has everything it needs to run but won’t fire and fills the cylinders with fuel. What could be my problem?