I threw STP in the full tank of Sunoco 94 Octane and after 100km(+- 50) of running, the half of the fuel is gone!
I don't understand what you're saying. It used more gas than normal ?
I use Cheveron Techron (the black bottle) with a full tank of gas. I see no reduction of power and no excessive use of fuel. I'd keep an eye on the performance with your next tank of gas. See if the power comes back and keep an eye on the mileage.