Your potentiometer on the pump is problably rusted sitting on long time with a low level of fuel (not protected by fuel).
I think it possible to change only the potentiometer but its trouble. (You have to do the same job as changing the pump + dissasembling the pump.) The other fact is if your car is over 135 k, it will be a good plan to change the whole pump because at this point it starts to loose power progressively until bugs appear.
However if you change the whole assembly, you have to be very carefull because Ford made changes on the gas pump all along the 4 years of production...
I have made a post about the gas pump differences year by year on discussion or maintenance sections in the last 3 years. (Sorry, I forgot precisely.)
The differences can be a real bug if you don't mind about them. For exemple, the place of the pressure sensor changed like 3 times (one year, 97 or 98, is on the top of the pump rather than on the tank...) and wire of the pump going to it has the exact lenght for it. Then, a wrong year = wire too long or too short...
IIRC, I put some photos on the post to help understand the differents setting.
But it's doable, good luck,
