2005 2.7D auto box problem. PO830, PO835?

Over the last 3 years that I have had the car I have changed about 2 litres of transmission fluid about every 6 months and gotten over the jerky acceleration going uphill etc.

I now have another problem. I had driven about 200kms and I accelerated to pull out and overtake, the box changed down quite hard.  I continued and some kms later did the same again this time there was the hard change and a message "Gearbox Fault" I stopped when the next rest area came up. Switched off and back on, no message! Took it easy for the next 600K, downchanges were not very smooth however. Got the Icsoft on it and got the following DTCs on the transmissinn 5th gear malfunction and PO830 and PO835.  Gear changing is not very smooth and there is a tendency to stay in 5th and not change up to 6th unless I lift off the accelerator a bit.

Anyone else had these probs?

M