My best guess would be that at 4,500 rpm's, the valves are floating due to fatigued valve springs.

To isolate a fuel flow problem, first change all inline fuel filters from the tank forward and make sure there are no kinks in the hard lines. Change all rubber connection hoses, no matter how new they look from the outside. The rubber INSIDE the hoses could be separated from the fabric cord and causing a restriction. Next, unless you want even more grief in your life, replace the bronze filter in the Quadrajet with a new one.

Beg, buy, borrow or steal a MECHANICAL fuel pressure gauge and mount it temporarily on the cowl just in front of the windshield with duct tape and tie wraps or whatever. Using brass ferrules and copper line, run a fuel line from the gauge to the carburetor right where the supply line goes into the carb. A trip to the hardware store for brass fittings and a trip to the auto parts store for a couple of pieces of rubber fuel line will allow you to fab up a temporary connection to tee off the supply line. Now, make some runs down the highway and watch the pressure. You will need no more than 6 psi and no less than 3 psi. If it's more, install a pressure regulator between the pump and the carb. If it's less, use a different pump and larger fuel lines from the tank to the carb. I've seen Denny post on here that the minimum size for fuel lines should be 3/8" and I agree with him. Guys who are going to drag race usually change to 1/2" lines.