I had never floored mine until last weekend. When I did (in 3rd and 4th gear), it was like it was farting or something while trying to top out, kinda airy sounding. Like it was trying to get there, but something just ain't right. It's all stock with a more modern Holley carb on it, as my 780 carb is getting rebuilt. As far as I know the wires and plugs are good, but will check the plugs soon. It's always hard to start though, after setting for a week or two.I just went thru this recently, but my fuel pressure would only drop during hard accel, freeway on ramps. "Spirited driving" usually, but sometimes just cruising on the highway.
Pulled my hair out checking the fuel filter, changing pumps, etc. I disconnected the fuel line at the carb to drain the tank and when I turned on the pump, it barely trickled out. Turns out my Earls sintered bronze filter was full of non visible crap causing a restriction. Threw in a plastic see thru unit and it ran like a champ.