2013 F150 Supercrew Platinum Ecoboost w/ 900miles. I get a puff of black smoke out of tailpipe when I accelerate or step on it for a down shift. Normal?? similiar to the "puff" from my '99 F250 7.3L Powerstroke. also....anyone feel the rear of truck "shimmy" at LOW speed? Less than 15mph. feels like someone is pushing back n forth on box.(side to side)