Are your coils grounded to the cylinder heads through a dedicated ground to each head like Holley has in their diagrams and what is grounding the block? I have a 2/0 ground cable from the block to a bolt on the front frame. Another 2/0 cable runs from the battery to that same bolt. I also have a motorplate but you can’t rely on those as a good ground.
Since that’s a factory Holley harness, it should have the shielding grounded at the ecu and if it was a wiring issue it would’ve gone away when you swapped harnesses.
