1989 Ford Econoline Wagon fuel system tips wanted

I’m having trouble in my fuel system. My van stalls and will not run when I switch to the rear tank. When I turn on the ignition I can hear the fuel pump power up. I have changed the fuel filter. I have also inspected the tank selector valve to see if the valve was switching between the ports but did not replace it. It also seems to have a low idle. When i start to go, if I give the van a very little amount of gas it almost wants to stall. Any tips would be helpful. Thank you for reading.

My GUESS , if both these symptoms happen when using the rear tank the pump is not putting out enough pressure. Test the pressure readings from each tank. It could be the selector, but those are pretty simple, I suppose there is a possibility it is at fault.

I will try that. Thanks!