fuel pump pressure

I have my fuel pump isolated pumping to fuel pressure gage only it pump to about 70it psi and then starts dropping should it hold pressure or is that normal for it to bleed down it has a new delphi pump i kept the old pulsator in there could that be leaking by

you need to test it after the regulator and should hold presure

Oh I know that to test regulator but when I put my new pump in I installed the old pulsator that sits on top of fuel pump and was reading on here thar I with couldve done away with it and once I do does the pump have its own check valve to hold pressure if you isolate the pump