I think you are right, unfortunatly one of my vehicles is programmed only to "lockup" at 50mph. If I dont get over 50 it will NEVER lockup. Its possible to reprogramm the Transmission to lockup earlier and even short shift. I wish more cars would have transmission modes, like economy and sport. of course manual transmission cars dont have that problem...

That's CORRECT !

I've driven many vehicles, trying eco-driving and the most efficient speeds are 47miles/hour (80km/hour) and ABOVE !

Ford Excort - Manual 5th gear does not work well below 40mi/h .
My Volvo switches to overdrive at 47.5mi/h.
My Chrysler Town&Country switches to overdrive at 46 mi/h. It has fuel calculator, that shows the most efficient speed at 62mi/h.

But if you drive at the limit, automatic thransmissio switches back and forth, using more energy. 50mi/h+ is the answer.