Fitech Fuel command Center Modification

I'm using the Fitech 800 HP system with the Fuel Command Center. I did the modification to it that was is on Youtube. Make the vent a return line back to the tank. Take the float out and take the brass screen out of the vent fitting. It works but what is happening now is. When I turn the key on the pump comes on to bring the fuel up to 58 psi. If I wait until the pump shuts off then it starts to loose pressure. I let it run for a couple of seconds then hit the key. It will start and every thing is fine. Just don't know why it is losing pressure now that I did the modification. It held pressure before the modification. Just wondered if any one else has used Fitech and ran into the same problem thank you