ST184 Gear Box has no overdrive....plz help

[broken-celica]

He everyone i have just done a engine and g/box swap from a 91 celica into my 93 model. Now the car was working sweet for about a month or maybe more after the swap, but has now decided to not select overdrive most of the time.
It selects overdrive when left sitting for a week or so, but after about 30 minutes tops it clicks back to third gear..
Would this sound like a solenoid issue?

[thechuckster]

fluid level in box OK?

One would expect a solenoid to work or fail and stay failed.

Most ECU-driven auto boxes will not do some stuff (lock the torque convertor for instance) if it thinks the motor isn't warm or the revs are under a defined limit.