Not that I can tell. I put on some Gibson exaust at the same time. Don't think that really made much difference either, at least not enough to "feel". If you put it on a dyno I bet you might see a couple ponies with those mods together. But from what I can tell, it just sounds a little deeper for the most part. If you want more power or better milage, proper gearing is the way to go. Stay away from throttle body spacers and chips too....they are a waste of money on the 4.0 liter.
2012 Rubicon JKUR: 4" Tera Flex Long Arm, Fox 2.0 Shocks w/resi, Fox Stabi, Yukon 5:13's, Evo C gussets, Evo Magnum Sleeves, Evo Rockstars, LOD Stubby Bumper, Poison Spyder Rock Brawler Rear Bumper/Carrier,Poison Spyder DIY Sliders, Poison Spyder EVAP Skid, KMC Strikes on 37" Nitto Trail Grapplers