I am having fuel flow problems with my Challenger. When  the car sits for a few days. I can start the car and have about 4psi on the fuel line. I will take the car for a hard run and the pressure will drop to 0 psi, just barely enough to keep the car running. At hard acceleration the car will act as if it has run out of gas. I have a electronic fuel pump on it. I need recommendations, fuel sending unit, fuel lines, or tank replacement?

You could have more then one problem, the first place I would start would be to replace all the rubber lines from the tank all the way to the carb the lines may look okay but they will start to flake inside and can block off the line, also some times the inside will collapse and stop the flow.

If the problem is still there look at the pump as it might be over heating and not putting out the proper pressure. If this dose not fix the problem let us know, also replace the fuel filter.

That's some good advise. Also I would pull the fuel sender out and check out the inlet screen.  It could be clogged. If you really have a 440 in it, go to a 3/8 inlet on the sender, and replace all the 5/16 tubing from tank to engine. 5/16 fuel line does not have the capacity to flow enough to make 400hp. Before i changed mine over, I could run my 360 out of gas at 65mph at WOT from a dead stop!!! Also do a vacuum test on the inlet side of the pump, it should be able to pull 5hg, on the outlet it should be able to pressurize from 5 to 7 psi. Stock fuel pumps from mopar usually flow 40gph. High -po ones are usually 80 to 110gph. Going to a 1/2 fuel line would be better, from the pickup in the tank, to a distribution block in the engine bay, from that go to a 3/8's if it's a Thermo, or two 3/8's if it's a dual feed holley. Better upgrade before you melt down. Might I suggest going to Barry Grants website for technical info on fuel requirements for your given engine. Remember 3/8 as the minimum in fuel line size on all Big blocks and 3/8 for hot smallblocks.  Good Luck