For intermittent electrical problems, I have hooked up a LED idiot light to different points on the suspected circuit to find where the failure point is.
In your case connect a LED across the fuel pump. This will tell you if it is getting power during the failure. If the LED goes out at the same time as the pump goes out you then know the failure is something other than the pump, if the light stays on but the pump goes out then the problem is the pump. each time you verify a component with the LED, move the LED to a different part of the circuit.
There is nothing tougher than finding an intermittent issue, especially while on the road.