When you go WOT (Wide Open Throttle) and power drops off, it's a good sign of a plugged exhaust. Possibly Catalytic Converter if it has one, but it can be Muffler, crushed/collapsed pipes, or a plugged screen at the end of the tailpipe. Listen to the exhaust at the tailpipe. If it's more of a wheeze than a pulsation, another sign of stoppage.
If your 454 is old enough to have a distributor vacuum advance, it might also have centrifugal advance under the rotor. Look for stuck, rusted, broken or stretched springs. Check for free movement of the weights.
