You might try tapping it in towards the frame to loosen it, then push it back through. If that doesn't work, take the nut off the bottom the pedal where it attaches to the arm, then give it a goo solid stike on the side of the arm where the pedal rod goes through it. It's just like breaking loose the taper on a tie rod or balljoint. Don't it it on the threads, as that will damage them. Once the pedal part is separated from the arm, the entire assembly can be removed from the truck, allowing for easier access to the pivot pin.
