[68c10airstream]

Welcome aboard! Late model gm is using a pulse width modulated control of the fuel pump. The advantages are longer life for the fuel pump and less drag on the alternator at times. As an example, say you are going down a mountain region and you are off the throttle for extended times. Pretty much all manufacturers shut off the injectors (or it would backfire) and on newer engines they shut off the fuel pump. Early ls engines would still run the pump but the return line prevented a dead head condition. The single (returnless) fuel system brought about shutting off the fuel pump during decel. Makes a lot of sense to shut off a pump that is dead headed!

I,ve noted fuel pressure changes on newer gm engines during idle cold and warm and hot restart because before i clean injectors i tap into the system to be able to match the pressure when i shut the pump off and isolate the fuel line and then pressurize my concoction and inject it into the fuel rail. I was surprised the first time i found this out.