Given the brake booster itself has vacuum, being pulled FROM one side of the diaphragm, how will it pull gas in to doom the diaphragm? I am missing something.... I'm trying to figure how it could pull fuel into itself. There is vacuum in the large line, engine running. Step on the brake pedal, and a valve opens, allowing the vacuum to pull against one side of the diaphragm, helping to push the master cylinder rod and apply the brakes. Foot off, the valve closes, and no more vacuum, no connection... Still in a bit of question on how fuel gets in.
Could the throttle position sensor be mal-adjusted, giving the ECM bum info?
You can have proper fuel pressure, but if the flow is restricted, it will not have enough fuel to operate the engine above a certain point.
Did you check fuel delivery volume? Jumper the fuel pump relay after connecting a gauge with a diverter to the schrader valve. Run the pump for a measured minute(or do math) and figure the delivered volume captured in a container with measurement marks.
tom