Many times a backfire will blow out a Holley power valve. If you have a spare, run it and see if it changes anything. With the PV blown you will be dumping fuel all the time.
That'd possible but that Holley would have to be about 21-22 yrs. old or older for that to happen. In the early 90's Holley incorporated a one way "anti-backfire" valve in the baseplate of their carbs that prevents a backfire from blowing the power valve.