I just spent a couple days driving on my tuned TCU I got back from Joe this week for my '15 Cayenne. Couldn't be happier with the results. While USPS Priority took a week to travel only a 5 hour drive away, Joe turned around the tune quickly and graciously sent it back 2nd day back.
Most noticeable is the shift pattern while the car is warming up. No more hung shifts and holding high RPM. Very happy with the performance regained.
I was able to remove and reinstall the TCU without removing the seat but just moving it up and forward. From there, you pull the carpet up and stick your arm in to feel the TCU, press the release tab on the sides and pull it out.
I'll bought a spare TCU (0C8927769AG) that I will be putting up for sale on eBay unless someone here would like to buy it.