I have also seen in the fuel tank in line with the fuel pump there is a device call a pulsater what it does is absorb the fuel pulses. Its about 3 to 5 inches long and is a hard plastic shell with a rubber insert that the fuel goes through. I have seen many crack the rubber insert and that would cause the fuel pressure to bleed-off after shut down.
Not all trucks have them but most do. That might or might not be your problem just keep it in mind.
Thsi could be found by doing a fuel pressure bleed down test
Good luck
Fireplug