Had an aFe CAI Stage 2 on my 2003 Ram 1500. When I traded it in on my new 2011 Ram 1500, the aFe CAI was the first thing I purchased for it. I was able to install in myself fairly easily. And that is saying a lot. A little improvement in mileage. Definite improvement in performance. And a great rumble on WOT.
Then this last Friday I had a MagnaFlow CatBack Performance Exhaust System installed. Everything the CAI improved the Exhaust System multiplied the improvement.
But as I keep telling my wife - "I am doing all these things to improve the truck's fuel efficiency. Any performance and sound gains are purely coincidental and completely accidental."