Did the shop install all new pipes from the cat back? what size is the stock exhaust leading into the stock muffler?

 

Yes it is all new pipes from the muffler back. It is 3' in and dual 2.25 outs.

 

your cross-sectional area of your dual pipes is 7.95 in^2, where your stock single 3 inch pipe is 7.07 in^2. So at any given instant, more volume of gas is being allowed to pass through your exhaust through the dual pipes.

So the pipes aren't restricing any flow based on their diameter alone.

 

Either on the sticker in the glove box, or check underneath on the axles, they have a sticker on them (may not be readable anymore).
Or send your VIN to Chrysler.com and ask for a built sheet, you usually get an answer within a day or two.