Stalling and loss of power

We need to start with fuel pressure when this stalls. It should be 50 PSI pretty consistently even when you are accelerating. It will move around a little but not much.

https://www.2carpros.com/articles/how-to-check-fuel-system-pressure-and-regulator

I would not worry about trying to check the pump with the bed off. Basically, we just want to know if there is power and ground. However, we pretty much know that is ok except if the pressure is dropping when it stalls.

Then we need to find out if the relay is cutting off only if the pressure is dropping. If it is not, then the pump is not the issue.

At that point we need to move onto ignition cutting off. This is most likely an issue with the ASD relay. But with this we will need to monitor spark or fuel injector power when this stalls.

We can do this multiple ways but let's get to that after we confirm this is not a fuel pressure issue.

Let me know what you find. Thanks

Okay. The standard for this is when the key is turned on one time it goes to 50PSI and then it should hold pressure above 30 PSI for at least 3 minutes.

If it cannot then the pump is the issue, or you have a leak somewhere in the system.

However, when you say you replaced the pump and not the entire assembly, I assume you did not replace the regulator as well?

More than likely this is a regulator issue or relief valve is stuck open.

What happens is the regulator allows the fuel to return to the tank and no flow to the injectors. This causes pressure to be low until the regulator opens enough to all the fuel to build the pressure.

Then when you shut the engine off, the pressure bleeds right back into the tank.

We could have other issues but if it were me, I would replace at least the regulator. However, at this point I would put the entire assembly in there, so I didn't have to go back in.