1998 Mustang V6-ghost problem

We purchased a '98 Mustang last year from a Mom and Pop dealer. The cluster would work one day and then the next freak out and quit. We took it to a Ford dealership who said it needed recalibrating. Now, we have a phantom in the power to the gas tank. We think it may be a relay, but do not know for sure. Can anyone shed some light on this? Has anyone else experienced this? Thanks!

When you problem with the power to the gas tank, can you describe that more? Do you hear the fuel pump prime or no, or just sometimes?

There is a fuel pump relay that controls power to the pump and a ECU relay that controls fuel to the motor after the pump. That would be good starting points.