Issue with crane cams hi-6 cd ignition

Cheaper it is, to disconnect the rev-limiter. If the engine continues to rev past 2500, say to 4500, and does so under load, then it's hardly likely to be the coil.
I have seen it be the plugs tho. Some coils cannot spark more than .028 gaps, some can spark .080s or even .100. Sometimes the timing is too far advanced for the fuel, and detonation cracks the insulators. Then it does exactly what yours is doing.