Hello, I am John, a Ford dealer technician.
I hope I can help solve your problem quickly and accruately.
The fuel pump relay is located under the plastic shield on the air cleaner support bracket. It should have a yellow, red, brown and tan/light green wire going to it. It sounds like this may be your problem. If not let me know and we'll go further and figure it out.
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There are alot of relays in these trucks. pcm power, wot cutout relay and others I can't name. I only worry about them when something stops working then find the problem!