I have a 99 model when i start it, it dies then when it does start it stumbles. I checked the fuel pressure at idle it carries 10 pound. At 2800 free reved it holds 7 pound, at full stall 2200 it holds 5 pounds. I think it may be a regulator or check valve problem since it only stumbles after it sets for a while. I am not really sure where the regulator is and if it has the check valve built it or not. Thanks

 

Get codes read with a scanner. Don't believe LP pressure is your porblem.It might be appropiate to have a live scan of sensors When problem occurs.
Might try a apps reset.