I put Gibson single exhaust which has a great sound to it and an Airaid intake on after about 300 miles plus new 18 x 9 aftermarket wheels. That first tank of gas I got 15 mpg in 4 dr sahara hard top 4wd auto. Next tank I got closer to 16 mpg. Next tank about 16.5 and now I am averaging about 17 to 17.5 mpg with mix of city and highway driving in Houston. How much is due to just breaking in and how much due to aftermarket accessories is unknown, but my but dyno tells me it has a little more kick on the highway when you punch it and pass someone.
Some people argue that CAI and exhaust don't do much for you in these dodge/chrysler/jeep vehicles that don't use mass airflow sensor systems, but I think as the computer adjusts to air that may only be slightly cooler and a less restrictive exhaust it does begin to map differently to the fuel air table in the computer and small gains are obtained. Is it worth the money??? I had an 04 Durango Hemi and still have an 06 Charger RT Hemi and on both of these installed Magnaflow exhausts, CAIs, and on the Charger used a Superchips tuner. Both perforformed better and from 3k to about 10K the fuel effeciency improved on both by about 2.5mpg overall from 3k to 10K. A friend has an 08 Charger RT stock with 5k miles on it and we switched for a day as an experiment and we both agreed that mine has a lot more pep and I average 17.5 mpg around town and he average less than 14.5 mpg. Do the math and it cost me $1k for it all and after about 35K miles it had paid for itself in fuel savings. Is it the best return on investment - probably not - but it is a lot more fun to drive!