Is it safe if I do the ECU tuning for my GTS 2013 ? will it hurt the car in the future "after 2 or 4 years " ?
How much power are expected if I do the ECU ?

that is very important question, I want to know the answer too

when I asked the same question they told me it's totally okay, it's just changing how fuel and air goes to engine, and car manufacture "Porsche" always limits with gas consumption per mile to compete in market against other cars,

I also found out that if your cars is not Turbo, tuning is not that big change in horsepower and torque,

however, until now i didn't find any well known company tuning Cayenne GTS 2013, they did the turbo only,
let me know if you fond one,