5.3 LS fuel pressure drops/ hard cold starts!

[Sonar Chief]

I would like some advice on my truck 5.3 based 1500 GMC seems the fuel pressure is inadequate to start the truck after it sits overnight! I rented a fuel system pressure tester. With key off, engine warm, fuel pressure is 59 psi and it starts right up w 55 psi running at idle. Turn the truck off and the pressure drops right away, within 15 minutes (went in the house and came back out) the gauge read 0 psi. GM bulletin says if it loses 5psi in 3 minutes to TS pump assembly ... or vice versa!

Cold starts ... fuel pump kicks on, and the starter just turns (like no spark) off/ on/ start multiple time. FIGURED OUT if I prime the system on/ then start w the accelerator pressed down the truck would start (blow excessive fuel out the exhaust) and idle normal and run just fine for the rest of the day warm. hmmmm!

Knowing now this is a return-less fuel system seems the fuel pressure is regulated by the ECM via the pump and there is a check valve inline that is supposed to keep the pressure at the rails. There are no codes on the SES and the truck runs just fine, no stumbling, or rough idle ...

There is no leaking externally, and based on the pressure drop rate I wouldn't expect fuel injectors, assumption good or bad? Seems GM put everything associated with the fuel system in the Fuel Pump Assembly ....grrrr.

Anything else I should check before I drop the tank and replace the pump assembly? Is the fuel pump filter part of the assembly?

Any help would be appreciated!

Michael