Fuel Pump Quits

I have a 2000 Chevy Express 3500 5.7 with 465,000 miles. Except for regular maintenance, the drivetrain is original. The 4th new fuel pump was installed yesterday (5/4/2007). The van will run for a while--up to an hour, and the fuel pump turns off. All electricals--including the fuel pump relay--check out and there is voltage to the pump when the ignition is on. However, the new fuel pump will run and then stop running, even while the ignition is on.

Please help, as this van is my income.....

Thank you in advance for any help you can give.

Check the fuel pump wiring plug in at the transmission cross member.
The have a habit of losing power to and threw and out of this plug in.
When it quits check for lose of power in that area.
Or at the fuel pump power feed where it goes into the tank and do not forget to check the fuel pump ground.
MT