I know you said you replaced the fuel pump, but mine was doing the exact same thing a couple years ago. The check valve went bad in the fuel pump allowing the fuel to drain back into the tank. Easiest way to check is to hook up a fuel pressure gauge. Start the truck, watch the gauge, then shut the truck off. The pressure should hold. When I shut mine off, I could watch the pressure drop to zero. Based on a lot of internet reading it's highly recommended to only use delco or delphi pumps, the knock offs don't last.
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