After installing the programmer, intake and exhaust on my HEMI (The Big Three), my highway mileage improved 4+ mpg and I don't drive it slow. I suppose if I set the cruise below 75 I'd get even better mileage.
You can see the before and after dyno results in my Ram Mods link below, pg 2.
My around town mileage has improved by 3 MPG.
Remember, if you are bringing more air in, it's a good idea to move more air out. Even a muffler change to a freer flowing unit will do the trick. You don't need to do a full catback. Without a freer flowing exhaust, you won't see the improvements in performance and mileage the "Big Three" will get ya.
Most CAI's will do the same thing. I run an AFE but the Mopar accessory cold air intake, a K&N, or Volant will do the trick. Just don't get one of those cheapy eBay things. They have really cheap filters that come apart and you'll end up with pieces of it in your engine. Also, the tubes are cheaply made, and don't locate the IAT sensor in the optimum spot.
Here's a great thread put together by RootBeer on CAI's that some good info on CAI's that will help you make your buying decision: