You have the 722.6 transmission fitted and the most common fault is the transmission electronics plate, but a code readout will confirm or deny this.
When was the transmission fluid and filter last changed?
I think you could be right, even though I sorted it myself last night, I dont remember when the transmission fluid was change because the service mechanics never mention that part of the car to me.
This is how I sorted it, for now...
I disconnected the battery, warning!...dont close the boot door as battery is at the back, I accidentally did that and afterwards thought "oh fk!" lol, pulled out the manual key but the boot key wouldnt twist somehow, good thing I got the driver door opened and crawled into the boot from the back seats and re-connected the battery.
Took it for a 1hr spin and WOW! it was like brand new! drove very smoothly and much faster!
However, I think this will be temporary, and gradually will go off calibration again over time, and I reckon its the speed sensor or plates like you say.
so, I'll drive it for another few days and see...