I have a 95 F-150 with the 4.9L and last spring I replaced both fuel tanks and replaced the pumps with used but good OEM ones, after a while I started having issues with it. When I go to start it after sitting overnight, it often cranks and sputters for about 5 seconds before it starts. Once it runs for a couple seconds though if I shut it off it will fire back up no problem (loss of fuel pressure?). Something it will also do is when the engine is warm after driving it, if I go to start it it will run for about a second and then drop down in RPMs for a second sometimes it even stalls when this happens, but then I’ll try to start it again and it’s fine. It also tries to die for a second or two when I switch tanks while driving not sure if that’s related to the problem but figured I’d throw that in. I run it off the front tank most of the time and it’s usually at half a tank or lower, it doesn’t seem to have the cranking after sitting issue with a full tank but it still stalls when warm starting. Not sure what the cause of all this is but if anybody knows, please let me know

 

When you go to start it in the morning, cycle the key between on and off a couple of times before starting, see if that helps.

 

Without empirical values for fuel pressure under the varying conditions you are just guessing. Rent or buy a fuel pressure tester.