Weak fuel pump?

Having a fuel starvation issue. 1948 F1 pickup, mild 350 sbc. Properly set up qjet fed by 3/8 steel lines and a napa mech pump. Gas tank, new, in stock location (behind the seat) with the fuel pick moved from the bottom gravity feed to the top so the pump sucks fuel from the top of the tank via a pick up that reaches to the bottom. Tank is vented. The truck has less than 1000 miles on it with all the fuel system new, filters etc. Run through the gears shifting at 4k to 4.5k rpm it's fine. Run it over 5k and it starves. It seems that a stock napa pump should be capable enough, but heres a twist. The top of the tank is 36" from the garage floor, the tank is 18" tall. The fuel pump on the motor is 16" from the floor, two inches below the bottom of the tank. Could the pump be struggling to lift the fuel 20" before it drops to pump level? If that's the case, I could always abandon my top pick up and switch back to the bottom feed, but I like the safety of the top pick up. Opinions, please.

 

I would change out the fuel pump to see if that solves the problem.

 

Is there a vent on the gas tank or cap ?

 

What carb/carbs are you running?

 

check float level

check for a plugged filter or kinked line or other obstruction

check fuel pressure before carb

I kinda doubt the pump is the issue

 

Clogged filter ?

 

it is either an improperly vented tank, which is easily diagnosed, by simply opening the gas cap when the symptom occurs, it may sound like a can of pop, or simply take off the cap and run her through the gears.

Or your pump isnt pumping enough, not necessarily a bad pump, but I think your fuel line is a bit small.

Or it could be a weak coil.