Mike, thats not entirely true, the motion of the front does cause the bump steer only if the drag link is not where it's suppose to be. The amount of spring travel or the number of leafs has nothing to do with the steering, assuming the steering and all adjustments are correct. On these trucks, the axle travel has pretty limited travel so it still comes back to either caster, toe-in or geometry of the steering links.
Not to be a pain, but it's caster that makes the wheels return from a corner and what keeps it going straight, toe-in also does, but the caster angle is the more important one of the two. Go back and look at the picture two posts up, the arc of the drag link needs to follow the arc of the springs as closely as possible. If you start out with the drag link at either end of the arc, you get bump steer, even with a dead on everything right front end, you still get some bump steer, it's just the way they work.
