This and the first picture are not of my car. They are from a 2006 RT with a Hemi.
My car only has dual untill exhaust about half way back.
My tires are 215/65-17 the ones in picture are 225/60-18
The little black thing by the rear bumper is to help deflect the wind from catching the bumper cover.
Here is a picture of the little black thing on the rear
Again not my car. This is another of the parts Dodge dropped on latter modles to save cost.
Thinking also of bringing the belly pan back to the rear of transmission.
a very important step to good aero is how all parts on the bottom of a car are l positioned... it seems they made the effort to align everything so the overall "landscape" roughly follows the line you'd want the air to take... some car have exhaust ans suspention componets etc hanging out in the flow...