04 tahoe hard start after sitting

04 z71 5.3 auto flexfuel hard start after sitting installed new delphi pump and filter with no change the problem is bleedback of sometype if u cycle the key(so the pump builds pressure) it starts rite up next step maybe pressure reg but i dont want to start replacing parts for no reason. only had truck since feb and had to install new dash cluster , plugs , fuel pump, filt , all fluids, i have no issues other than this now it has 110000 miles on it now had 98000 when i got it and nothing seems to effect this except time as it is getting worse there are no codes so any one who has had this prob please help thanx

04 z71 5.3 auto flexfuel hard start after sitting installed new delphi pump and filter with no change the problem is bleedback of sometype if u cycle the key(so the pump builds pressure) it starts rite up next step maybe pressure reg but i dont want to start replacing parts for no reason. only had truck since feb and had to install new dash cluster , plugs , fuel pump, filt , all fluids, i have no issues other than this now it has 110000 miles on it now had 98000 when i got it and nothing seems to effect this except time as it is getting worse there are no codes so any one who has had this prob please help thanx

Engine Hot or cold sitting?

What is the fuel pressure doing?
The 5.3 is known for bad fuel pressure regulators.
Any gas in the vacuum line at fuel pressure regulator?
Any black smoke after hard start?