[decooney]

Getting a professional tuner involved is the way to go especially when you are at the point where you don't know what the root cause is and you are ready to throw a bunch of new parts at it.

If you have a smallish Holley running on your 428, with more open and flowing ERA sidepipes, it could be a lean stumble in the transition circuit, or a combination of fuel and timing advance needing some fine tuning by a professional who is great with carbs too. A good tuner will get you going in the right direction with proper diagnosis.