[Johnnyvav]

I started with Borla Cat Back about $850 + $150 to install. Then Mopar Headers (came with Free flow Cats) for about $1000 + $500 (i think) for install.

The car sounded great and felt pretty good But then I pulled out my "drop in K&N filter" and replaced it with a DUB Cold Air Intake.

That really pulled the whole exhaust system together in both sound & performance. You can get a CAI for a couple hundred to a few hundred and it's an easy DIY install.

A complete system will make each part really perform. It doesn't really matter what order, just keep in mind you need:

1) Cat Back
2) Headers
3) Free flow cats
4) CAI (cold air intake)

Some more good bang for the buck, that you may consider starting with:
A stage 1 chip or (and preferred over the chip) a Superchips Flashpaq tuner.