Toyota Repair: 1994 4 Runner SE 6 cyl. AutoTransmission, transmission failure, impending trouble

Question
My 1994- 4 Runner SE Auto Transmission will not shift into 4th gear until the engine is up to operating temp. It is very consistant (since I purchased the auto 18 months ago) in that what ever the weather is (90 deg or 20 deg), it will not shift to 4th until the temp is up.
I have had the fluid changed.

Answer
This is a kind of common problem and it is normally the first sign of potential transmission problems, my own 1990 4-Runner has been doing the same thing for about 3 yrs but it's still OK other than it will chatters on hard acceleration from a stop which is a sign of impending trouble and sooner or later I will have to address this or be faced with a complete failure of the transmission, it does this at with regularity and always shifts into OD at the same spot on the freeway, about 2 miles, I have tried some things like replacing the temp sending unit for the ECU but it didn't help, sorry for the bad news but it is definetely I sign of impending transmission failure, just a matter of time.