The TSB for the GC's built before 7/14/13 worked well for smoothness on mine with a noticeable drop in mileage. On mine I now have to use the paddle shifters to get into 8th gear on the Interstates and I cannot believe my eyes for the mileage difference it makes. I have installed a K&N air filter and it makes a big difference in performance on my V6 but never seemed to help my Hemi's when I had them. So now I can use ECO all the time with a lot better performance and really smooth shifts. This is my 15th Jeep and by far the smoothest shifting transmission of all of them since the TSB installation.
15 GC Overland
15 Rubicon Unlimited