Need to upgrade Fuel System

Unless you have about a 9 second car it's not the size of the line

Your car came with factory "carbon can" IE evaporative emissions. If that has been removed, the tank may not be vented. First thing to do is go for a "hard run," stop and immediately remove the fuel filler cap...............see if there's a vacuum in the tank.

Next is to suspect EVERY part of the fuel system front to rear

Sender / pickup, whether new or old, suspect fuel sock / plugged

Hose connection at tank, old, crimped, collapsed?

Fuel supply line, rusted gummed inside?

Any hoses at suction side of pump

Pump itself.......read the shop manual, "there's a procedure for that"

Fuel filter after pump

Where to start?

Probably at the connection from line to pump inlet, as that's fairly easy to get to and divides the problem between the two ...........pump and onwards, and supply line and back to tank

Shop manuals:

http://www.forabodiesonly.com/mopar/showthread.php?p=1970088617

There's test procedures for pump vacuum, pressure, and flow capacity. I'd look up something high performance, like a 440-6 or hemi, and expect your pump to match that flow.

Use a vacuum gauge. The pump should be able to "suck" at least 12" Hg