your fuel pressure should remain at 50 to 60 psi and not drop off after the engine is stopped. you have a leaky check valve in the fuel pump and the fuel pump needs to be replaced. it takes 10 psi to start and 50 psi to run efficiently. I have the same problem with my 03 4.6L XLT, my friends brother is a master tech for ford in detroit and ran through the diagnostics with me. When I hooked up the fuel pressure gauge on my fuel rail and just turned the key the pressure would go from 0 to 8 when I would just turn the key, while cranking it would start at 10 PSI and after starting immediately go to 50 psi. after turning it off you could see the pressure slowly bleed off and eventually go to 0. A check valve will prevent this bleed off and hold the pressure at 50 psi. I now need the instructions for tank removal. My 03 has different fuel line disconnects that I'm not familiar with. I believe you squeeze them and pull the lines but am not sure.

 

I have the same problem. I've tried a MILLION fixes trying to avoid a fuel pump replacement. The check valve is part of the fuel pump. I'm told that it cannot be replaced or repaired. Have to replace the entire fuel pump to fix the check valve ($$$).
I will take mine today to have the battery tested. Hopefully v1uhoh is right and it is a simple (and cheap) fix.
I dread replacing the fuel pump.

 

Removed tank and installed new fuel pump. 2003 4.6 L XLT 2x4
step by step (adding to JeffHann74's excellent advice)

1. removed spare tire per to allow more room

2. blocked front wheels and applied parking break

3. disconnect negative at battery

4. Jacked up drivers rear using jack that came with Expy this allowed me to put jack stands under the rear frame and under the frame below the drivers seat.

5. loosened and removed the hose clamp attaching the filler tube to the tank spout, I think it was an 8mm socket, flexed hose and removed the hose from the tank spout.

6. removed the fuel filter cover and removed the 3 fuel filter line. these have blue connectors that you pinch and then pull the lines out (very easy).

7. in the front of the tank (by the drivers seat against the underside of the floor) there are two fuel lines one large and one small. the large one had a green connector that I squeezed both sides and pulled this connection apart. The small line with a purple connector I left connected because it is connected to the fuel filter and has enough flex to not interfere with tank lowering. both these lines are attached by a plastic holding clamp in front of the tank. pop the locking tab off and remove these lines from the clamp. You will notice the small line is also held to the tank by a plastic yellow squeeze holder. I pulled the fuel line out of this.

8. Placed my hydraulic jack under the tank with a piece of wood between the tank and jack and raised it until slight pressure was applied to the tank.

9. took a 1/2 inch socket and extender and removed the back strap and then the front strap.

10. removed the front strap from the truck and left the back one dangling.

11. began lowering the jack and the front of the tank about 4 inches. you can now see the electrical connector to the fuel pump. disconnect this.

12. lower the tanks another 3 or 4 inches. the back of the tank will rest on the stabilizer bar. there is also a 3/4 to 1 inch hose attached on top of the tank near the back drivers side tire, I did not remove this. it has enough flex to get the job done.

13. You should now be able to see the pump with a Jar lid looking screw down holder on it. you will also see dirt and debris in the depression on the tank around the fuel pump. get compressed air and spray this clean to prevent the stuff from falling in the tank when you remove the pump. If you don't have compressed air a hose and water would work.

14. get white out or some other marking paint and make a mark on the tank and Jar screw down lid. this will tell you later how far you have turned and tightened the lid when you reinstall it.

15. My screw down holder was on very tight and could not initially be unscrewed by hand. I took a rubber hammer and a wood dowel and tapped the tabs of the lid in the unscrew direction. after a few beatings, the lid began to unscrew and I was able to unscrew it the rest of the way using my hand.

16. Once unscrewed, carefully lift the pump out of the tank. you will have to manipulate it a little to get it out but it will come out. along with the pump will be the screw lid, two fuel lines which go to the filter and the pumps electrical connector. The pump is spring loaded and can be compressed a little to clear the way. make sure you have enough room to get the pump out of the tank and the Expy's floor above it. if not lower the tank a few more inches and it will come out. there is also a green rubber gasket that seals the new pump to the tank. it just lays on the tank when you remove the pump but make sure it doesn't fall in the tank when you remove the pump.

17. take the old pump and the new pump, make sure they match. disconnect one of the fuel lines off the old pump and place it on the new pump. Mine were attached with a purple connector that you pop the little hold down clamp with your fingernail and once open, squeeze the purple connector ends and push up. this will disconnect the line from the pump.

18. install the new green rubber gasket around the tank before you place the new pump in. the gasket fits in a groove on the tank opening.

19. place the lines on the new pump and maneuver the pump back into the tank. make sure you have placed the Jar screw lid over the lines and electrical connector before placing the pump in the tank. Be careful not to bend the float or damage the pump. it will take some wiggling to get it in there but be patient.

20. Once the pump is in the tank, you need to depress the new pump with one hand while slowly threading on the jar lid. I found it easier that way because I didn't have the upward pressure of the pump countering my downward pressure on the jar lid. Once the screwing down of the jar lid begins you can take both hands and turn the lid until its almost tight. this is where the white line up marks come in handy. slightly tap the lid on its tabs until the lid meets the line up marks you made in Step 14.
you can also press down on the new pump and be able to tell there is no downward spring action because the pump is now secured and tight to the tank.

21. Follow the direction in reverse to reconnect everything.

Took about 3 1/2 hours by myself. Empty tank (low gas light was on) do not do this with a full tank and no smoking. beers can be enjoyed afterwards. Also another set of hands would have come in handy and probably cut one and a half hours out of the job. I'm a shade tree mechanic and say this is not real difficult. just take your time and digital pictures if you can to remember where everything goes.
Hope this helps. cost of pump was $269.

 

Wow, I purchased 1 from Advance Auto for $50. (I think). Its been working for about 50 or 60k now!

 

$50 does seem a bit low. That aside, you can buy just the pump usually for about $100 but it doesn't have the sending unit. The whole assembly (pump, sender, strainer, etc.) is well over $200.

 

been a while, I know, but my 'hard-starting' problem was in fact the pump assembly. That was a fun job...