I have a 1996 90 series automatic Prado 3.0D with 250,000km that has started recently not changing up a gear. It will get stuck in second or third and never shift up. It happens randomly, both when the car is cold or warm, but more often when I am just starting out. Shifting into park, neutral, or reverse does not help. It will still downshift fine. Usually after a few km of driving it will then start shifting normally. I have tried with the OD on and off and also the PWR ECT button on and off and doesn't seem to make a difference.

The transmission oil was flushed about 10k km ago, and looks clean on the dipstick and at the correct level.

Would this be a solenoid issue? Is there a way to check the solenoids?

Thanks for any advice.