No power at WOT after 5 seconds

[Duro5341]

Hey guys....

I have a 86 K10, 350 Heavy duty emissions engine, TH400, 3.08 rear end

Here's the problem

I have lots of power at WOT for 5-7 seconds, then it falls on it's face, you let off the throttle and then give it alittle....nothing. Then after 15-20 seconds of coasting it's fine. I can feel the secondaries opening, and the accellerator pump squirts fuel when pumped. When just normally cruising around town it's fine, lots of bottom end torque, and idles, and starts up great. Just looses power at 75%+ throttle

It almost feels like the fuel pump can't keep up with the carb, and it's running out of fuel. The fuel pump looks a couple years old, but that means nothing....it could be a cheap POS out of the box, it was replaced by the previous owner. I haven't checked fuel pressure yet, but what should it be at with a bone stock(all original) 350..

Anyone had this problem, or have any insight...

Thanks
Duro