Toyota Landcruiser 100 series auto 5th gear lock-out

The gearbox was serviced at the same time as the new solenoid was fitted. Wiring connectors have been cleaned. I am not familiar with TISS or TOSS. I have been told that the clutch plate in overdrive could have glazed over from heat which in turn shudders when hot and trips out the computer, making it think that something is wrong, but on service of the transmission, oil was OK. The transmission had its first service when the fault was detected, if going by the manual it was not due for a service @ 130,000 just check for leaks...
It is getting to a stage where i cannot drive it without the engine management light coming on and forcing us to pull over and switch the engine off, then restart the car to reset the computer.

TISS = Transmission Input Speed Sensor
TOSS = Transmission Output Speed Sensor
I've no idea if the Tojo transmission has one or both but would think it probably does, probably called another name tho'.
In the GM transmissions the above sensors sense the input and output speed of the engine and the drivetrain to control shifts. They use a stepper ring and the sensor is actually a magnet which runs very close to the stepper ring, depending on how fast the magnetic field is broken by the stepper ring it senses the speed. Because they are magnets any metallic dust in the auto fluid is picked up and sticks to the magnet giving faulty readings. Easily fixed by removing the sensor, cleaning the metal off the end and reinstalling it.
Faulty sensor reading can do all sorts of strange things, from stopping overdirve being selected to in a worst case putting the trans in limp home mode.