100 Series LC Auto Not Changing Out of 3rd Gear

I am currently in Mitchell west of Roma QLD; a long way from home in Canberra.

My 2003 100 series Sahara TD auto is not changing up to 4th or 5th gear.

If I put the lever into 3rd gear and accelerate up to say 3500 revs and then take my foot off the accelerator the vehicle slows down and the revs reduce only a small amount.

If I put the lever into 4th or 5th gear the revs do not change from what they were in accelerating in 3rd gear, but if I take my foot off the accelerator the engine revs drop right back to idle speed. There is no deceleration, as if the vehicle is in neutral.

The vehicle did the same thing last year, but then the problem magically disappeared. I had no problem on our Cape York or Vic High Country trips since that time.

I have checked the LCOOL site and found roughly similar problems, with no consistent solution.

I have been talking remotely to an auto transmission expert who has given me some valuable information on running various tests (including resetting the engine CPU) to try to determine the problem; however it appears that it is either a computer problem or else a gearbox problem.

I have booked the vehicle into the closest Toyota Service organisation.

Has anyone else had this problem; if so then how was it fixed. It appears that I may be up for about $10k worst case.