Fuel pump and sender assembly

Hi, new here. I am repairing a 2000 Malibu with a Pontiac 3.4L for a friend that won't start. The no-start condition was traced to a bad fuel pump (would only start if I bashed the bottom of the gas tank, but wouldn't stay running). Replaced the fuel pump but it doesn't start still. It fires but won't turn over. Starts perfect with starter fluid but as soon as it's all burned it stalls. The fuel rail does not seem to be maintaining sufficient pressure to start the car. As soon as the fuel pump stops the pressure drops to unusable levels. With the fuel pump running I tapped the fuel rail valve and burped the air out. While doing this I noticed there wasn't very much pressure, more similar to a faucet running part open. I listened to the injectors with a stethoscope and they all sound like they're firing.

I'm starting to think I didn't install something right in the fuel pump assembly like a check valve or something (never did one of these before). I'd like to know if anyone has an exploded view of the fuel pump/sender assembly or can scan a page out of a chassis service manual so that I can confirm proper assembly. Any help will be greatly appreciated, this guy can't get to work without this car.