Originally Posted by 270
I joke not
Ok, to answer the question then, letting air out will only cause the truck to have a slight pull the that side. While you are correct in thinking it will 'straighten' the steering wheel, that will only be the effect of the truck steering into the ditch.
If you really don't want to go back to the alignment place, and the off center steering wheel really bothers you (I'm with you by the way, I hate that), then you could very carefully look at the direction the tie rod ends are threaded, and after loosening the lock nut, turn the left one a little further out and the right one a little further in. The effect of this will be to move the steering wheel more to the right as the truck is going perfectly straight. Tighten the locking nut, then test drive it, and adjust again if needed.
Do I recommend this method? Not really, because you may end up with too much toe in or toe out, but if you only move them a small amount, and in as equal amounts as possible, you'll probably be fine.