What makes you think its a fuel problem. Is the car nose diving when you put it to the wood. The first thing that comes to mind for me is are the secondaris opening to slow or fast. Did you change to a richer needle and jet combo. If this is the same carb that was on your 400 it may be way to lean for you 428. My brother just dyno a 455 and we gained 40hp from jumping the jet sizes up 6 numbers both front and back. This was a demon not a quadrajet but same principle. I would think it would be normal for your pressure to go down with the car accelerating.
