Dropped my 04 Silverado off at the shop last night since I didn't have the time or patience to diagnose the misfire. They thought they had it figured out with two cylinder misfires - replaced the coils and ran better, until it didn't. Put the two bad coils on other cylinders, they ran fine. Fuel rail pressure looks good, all other diagnostics coming back fine. We're scratching our heads collectively. They're wondering if there may be trash in two of the injectors, but I would have figured more than two injectors would be impacted. Plus, they ran a pressure drop test on each injector, and they all came back within spec. What the heck? Now I'm wondering if there isn't a coil harness issue, or something going on with the ECU.