Final feedback
OK guys, in for surprises ? The guarantee changed my logic board, no result; changed display, no result. Matter handled over to Apple engineering. Said it must be a software problem. I also agreed. About 15 days ago, out came the Thunderbolt Firmware updates (2 on the same day): voilá issue resolved.
Very glad with AppleCare, they just wanted me satisfied with the issue. 2 major hardware exchanges and they now have another 2 years guarantee. And now my first iPhone. All in one, great Apple satisfaction. Been with OSX for 5 years now. Windows pc´s are good for fishing, just put them in a fishing line and the bate will definitely go under water, nice for weights.:;P