Quote - "Also, why doesn't setting Forcelimits on x and y translation of the Piston keep it from wobbling?"

Because it is being constrained on it's x and y translations, but those translations are relative to the centre of origin, and the centre of origin is moving, because it is attached to a moving part. The only thing to do here is to increase the scale, your point at objects must be farther, the farther they are, the less you will notice this.

Ok.  I added Piston Target A and B; I'll move those forward.  Too bad there isnt a way to constrain it though.