Im not too familiar with the theft system, but did you drop your keys into water?(if it has a PATS key) Someone who is more familar with the antitheft system should be here soon, to help remedy your problem.
Also i wasnt aware of ford making a 4.8l V8.... anyways welcome to FTE .
I wonder if the anti theft device, is controlled by the GEM module?
Some of these trucks came with a faulty windshield seal.. which in some cases gets the GEM module wet, then certain thing start to go crazy.