In your night rail road jump test video when I watched it heard it sputter. . ALL the articles I've read say the 4.3 loves to breathe and you didn't mess around in your build. Remember I'm running a 500 cfm. I say it's lack of fuel and it's sucking the bowls dry.
The only time I heard it is when you were in high gear and WOT and when you backed off it stopped. Fuel.