Ok...it was not just a Tesselation problem :/
The game ran nice and smooth at 55°C until I visited the village of Saldannis. I spoke with Jemynon about a bandit hideout near their village causing problems. I accepted the quest, left the village and out of a sudden my GPU jumps to 100% usage all the time and the temperature skyrocketed.
I checked the options and everything seems normal. The right GPU was selected, no tesselation and everything like I had it before.
@Heinz Solo: I disabled the sound, but it changed nothing. I have no idea what causes it. Even two restarts didn't fix it. Maybe something in the village, the dialogue or the appearing hideout caused the problem.
Strange is, after the problem started, even just loading into the menu after a restart was maxing out my GPU.
Edit: e1.0.8 didn't fix it. Creating a complete new start isn't helping either.