I don't think anyone has said it yet, but a couple years ago I had similar fuel pump issues where it would just quit out of nowhere. I did the same fuel pump relay replacement, jumpered the pump on full time to test and everything would work. I would put the relay back in and all good for a while. Then out of the blue it would quit again.
For me, it turned out to be the connector in the driver side kick panel area. The power wire for the relay goes through this connector. What I found was the female pins had opened up and were not making good consistent contact with the male pin on the other side of the connector. A simple tap of your foot against the kick panel could cause the fuel pump to lose power - not a fault with the relay, just no power to the relay. To fix it I used a small precision screw driver to bend the two halves of the female pins inward and cleaned both sides of the connector. I haven't had an issue since.
I had to do the same thing with the pins on my power window switches as these were intermittent at times too. Worked great there as well.