Yes I have cruise control. The limp mode can start at any speed, often after just idling at a traffic light, or as I described, when overtaking at high revs.

Today I was lucky, driving 650 km nonstop in 28°C with no problems, but if I go out and start the car now after an hours rest it will most likely be in limp mode again...

To find out if the cruise control is a part of this, can I remove a fuse or what?

Edit: I did just that, restarted the car, it was in limp mode now, removed the fuse, no success...