running out of breath in the 1/4 mile

I don't know if a 15 second pass is pinning you to the seat, but if you suspect the fuel is uncovering the pickup, just get most of the fuel out of it. Then just jack up the front end about a foot and a half and see if the car will continue to run after a while. You didn't complain about first or second gear much, so it would seem to be getting fuel. If it goes into third and then recovers, why is that. Maybe the gear is too steep although I doubt it with the hp you are claiming. That means the problem could be the ignition not firing well when it gets into a heavy lug position. Just guessing though.