It's possible that the master cylinder may be bypassing, or leaking internally. With the truck running and in park, apply normal pressure to the brake pedal and hold it for a minute or two. Don't try to shove the pedal through the floorboard, just hold it as if you were normally stopping or sitting at a stoplight. Note any travel after the pedal has reached it's normal stop. I'm unaware of any recent concerns with this problem on the SUVs, and we don't see very many F150s in my neck of the woods. I'd still get your friendly neighborhood stealership to check on it. When I get back to work tomorrow, I'll do a little checking of my own.