Hi all, my memory was not quite up to scratch
I had the car out on the Monash over the last couple of days and at 110kph (actual by GPS) the tachometer shows a shadow less than 2000 RPM, so this agrees with Ian's findings. Any difference is likely due to tyre wear differences and manufacturer.
But I still suspect an actuator problem. If one of the clutches is slipping this will cause heating and when hot enough the transmission will shut down, probably with an overheat code. But it might take quite a time to get to that point - possibly quicker if you are climbing in hilly country.
And a comment re fuel consumption, I'm seeing an instantaneous figure of 5 litres per 100 km on horizontal road in still air - It actually hunts either side of that figure by a small margin. However as I nearly always check economy rates at each fill by calculation, I can say that the on board long term average is quite optimistic. At the fill before last I calculated a figure of 5.8 litres per 100 km and the car was telling me that it had used 5.4 litres per 100 km since the last fill.
Hopefully Ian gets the problem sorted quickly - it must be very frustrating wondering if/when the car will stop working on a long trip.
Cheers