My fuel pump stops while driving sometimes.

I installed a new fuel pump earlier this year and it recently started cutting off while driving. I have a fuel pressure gauge installed on my dash and the fuel pressure seems fine and the car works good as long as the pump is running. The car shut down on more than one occassion and after checking everything I decided to change the relay for the pump with an extra one I had lying around and was able to get the car started. I checked both relays and they seem to be fine because whenever the car shuts off I just swap the relays and it starts again. What do you think would cause the relays to malfunction?