Help Diagnose This Problem

[BigDave]

I have a completely original factory 402BB. The fuel pump, in-line fuel filter, and all rubber lines were replaced over a year ago.

Recently, after the truck has been running awhile and usually when the AC is on, I have been experiencing an engine power loss at WOT (wide open throttle). It happens more frequently when the AC is on but it has happened without it too.

I can be rolling down the road, slam the throttle, and near the top of the shift, the engine scavenges hard like it's running out of gas. If I let off and coast a bit until it recovers and re-apply reduced throttle I'm back where I was.

Again, from dead stops, at WOT near the top of shift it scavenges like crazy.

I know it has to be a fuel delivery problem. It sounds like the secondaries are just starting to open good and then, WHAM the bottom drops out of it. I was wondering if it could also be loss of vacuum. Recently I've noticed when I drive at highway speeds for awhile I have less brake pedal than when I started on completely cold brakes.

Any help would be appreciated.