GMC Repair: 2000 gmc 5.3 hard starting problem, psi drop, ac delco

Question
My problem is similar to another post. I replaced the regulator, fuel pump and filter with all AC DElco. Still hard starting. if you turn key on,off,on then will start. Trk runs fine. I put a gauge on the rail, when the key first on 60 psi but drops to 0 fast. When you start psi is 60 then drops nad holds at around 50psi. Any Ideas.

Answer
Hi
The dropping to -0- fast is what I see may be the problem.
Isolate the problem by pinching off the return line to the tank (there are special hoses made with fittings to close off, so as not to damage the hard rubber lines) Key it on. If the pressure DOES NOT drop, the problem is from return line to tank unit.
If it does drop  close off the pressure side (again, proper hoses have a fitting to check BEFORE and AFTER the shut off valve). If it holds the problem is in the rail, injectors or regulator.
If it falls it is the pump.
Entire fuel system diagnosis.
The 10 psi drop while running is normal, usually it's a bit less (4-7 psi) but 10 is acceptable.
I really hope this helps.
I wish I could do more.
Good Luck
Pawl