Eh, piston slap SHOULD go away when it warms up. It is just caused by the loose tolerances of forged pistons when they are cold. Once it is warm it should go away if the engine was properly assembled. That is why when we build an engine for someone we always recommend bore matching and going a little over (10 or 20 over) so that the cylinders can be matched EXACTLY to the necessary clearances. Drop ins are not the best thing in the world.