John,
Your profile says that you don't have a car.
Can you update it please?
As you're in Australia I will assume for now that you have a 2.5 litre KV6. If that's the case then you should check all engine tuning parameters. If you have never cleared the breather pinhole in each cam cover then do that as a priority. Automatic transmissions are very susceptible to engine tune often leading to incorrect diagnosis that the gearbox is faulty. In any case, in my experience the downchange during hill descent is very subtle. I wish mine would respond
more vigorously.
Simon
