An update on symptoms after this morning look: the gearbox is shifting gears higher, but at very high revs and very rough.
It looks like the main thing is too high pressure that we cannot adjust as it does not react neither to adjustment screw turning nor to rod lengthening.
Any clues now?
I had my automatic gearbox refurbished (reputable shop). We installed it back in the car. We went through the pressure adjustments by the book. Yesterday, after a couple of rounds we managed to adjust shifting - it did shift up and down just great, nice and smooth, kickdown working - everything great.
This morning my mechanic took the car for a ride. Made about 2 kilometers. Then from the standstill the car moved, shifted up to 3rd gear roughly and did not shift up anymore. It now shifts up but at very high revs and roughly.
We checked the pressure - it is high on idle, vacuum off, over 6 bar. It does not react to adjustment screw turning - neither direction. It does not react to the linkage rod shortening/lengthening - just stays high.
We have dismantled the diaphragm housing to see if everything is moving there - but it looks ok as far as we could tell.
Any clues what it might be?