Does the SES light flash when it's misfiring? My car did the same thing, ran fine but as soon as it added boost it misfired. I bought a used OEM coil pack from a junk yard for CHEAP and went through and swapped it out. Everytime I swapped one out I'd take it out and drive it, if it didn't fix it I put original coil pack back in and moved to the next one. It ended up being the last coil pack I swapped out, no more misfire and lots of power!

You may try using an HEI ignition tester to put load on your wires, coils and ICM. Here's what an ignition tester is, Part 1 -HEI Spark Tester: How it Works. Make sure it is an HEI one. Some autoparts stores carry them or order online at Amazon for around $10.

Good luck