my 240 is not getting enough fuel..

i can drive a max of 5mph then my car bugs out/gives up on the acceleration (engine still stays on)

i do have a fuel pressure regulator.
and i just changed fuel pumps recently (used) so im not sure whats goin on.

it can rev... but not pass 2k... for example..

if im on neutral and step on the gas and hold it... it revs then drops then revs then drop and so on.


help please?