Hi Alfskie and others.
Did you find the cause of this problem? as I am having a very similar issue.
My car has done around approx 80,000km. Up until recently I had very little problem with it, I had the issue were it would sometimes take a 2nd go to select reverse but from what I understand that is quite normal.
Then around 12 months ago it wouldn't take reverse at all, I had to select 1st for it to go into reverse, this happened a 2nd time but its only happened twice in the last 12th months or so. Around 2 months ago I had a major problem with the gearbox. The pin on the selector shaft broke. The gearbox had to be pulled apart and the part replaced as well as the 1st and 2nd selector and several other bits. At this time I also had the clutch replaced. About a month after the car was back on the road I was driving home in city mode doing around 60km/h. The system went to change to 5th and dropped into neutral. At this point I simply slowed to a stop and selected a gear and went off.
The next day I went to my mechanic and had the normal tests done which showed no faults and the pump working fine (correct psu), he also did a re-cal on the gearbox. About four weeks after that at a very similar time on almost exactly the same piece of road the problem happened again, only this time I was changing gears manually using the stick shift. Both times the problem occurred on the way home form work after the car had been parked all day and within 15minutes of driving.
It has been more or less 2000km since the work was done. My Mechanic is suggesting I need to do some more KMs yet, but I am not so sure. Does anyone have any ideas?