The GM ignition module set up fires both cylinders for every coil at the same time, everytime. That is to say regardless of wether it is time to fire cylinder 2 or 5 they both get the spark. It doesn't take much energy to fire the cylinder which is on the exhaust stroke, so for design considerations to keep the system simple it just fires both. So if you suspect a DEAD coil, or loss of input to the primary side of the coil both cylinders 2 and 5 will misfire or not fire. It is possible, though quite rare for a broken terminal at the secondary side of one of the two cylinders on the coil, either 2 or 5. But you can swap the coils easily with one of the other two coils for troubleshooting.
I agree nothing other than the plug wires so far could have caused your problem, but it's always good to check the easy stuff first. If you find that cylinder 2 and 5 are both misfiring, then you need to dig deeper into the iginition control sytem, including the computer, crank trigger, ect.
But I would start by asking is it misifiring under load only? Or worse under load, or does it misfire running at idle in nuetral? Also does it seem to mifire right from the start, or only after it's warmed up?
If it is misifiring worse or only under load, that is in gear accelerating, I would run a static AND dynamic compression check first, including the snap throttle check. This will eliminate anything mechanical with the engine, especially valvetrain items. Remember the static compression check only tells you the sealing condition of the engine, the dynamic check will tell you it's breathing ability of individual cylinders which is why this is the check along with the snap throttle test will tell you what you really need to know. The static test is only a baseline.
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