My truck is having a hard time starting sometimes. Sometimes it will fire right up and other times it will crank for awhile and then sputter to life. If i turn the key and wait for the fuel pump the truck starts fine. I am thinking my fuel pump or the checkvalve on the pump maybe going out. I have hooked a pressure gauge up to it and the pressure bounces between 49-50PSI. when i shut the truck off the pressure drops to 20PSI in about 15 minutes and holds at 20 psi. Im just looking for some help, do i need a new pump?

Truck is a 99 w/ 5.9

 

Bad check valve in the fuel pump or leaking injector(s).