Nissan Repair: 1993 Nissan Altima Drive in 3rd gear on highway, steep mountain road, nissan altima

Question
I don’t think it is a bad transmission, but rather the electrical wiring or possibly the torque converter that is causing shifting problems in my 1993 Nissan Altima GLE.  I say this because of the car’s history.  The previous owner replaced the transmission with a used transmission (not a rebuilt one).  At that time the car was experiencing the same shifting problems it has today.  There was a warranty on the transmission and I replaced it with another used transmission, but did not fix the problem.  In short the car has had two transmissions and the same problem occurs leading me to believe it is not the transmission.

Symptoms:

When driving at highway speed the car cruises in 3rd gear when on flat land, but shifts into 4th gear when going up hill.  So I drive at 58 mph because I can’t get out of 3rd gear.

The car accelerates fine, shifting from 1st through 4th gears, but when I let up on the gas at highway speed it shift down from 4th to 3rd gear.

I cannot manually shift the car into 1st or 2nd gear.  When I set the lever into 1st or 2nd gear manually, it operates the same as Drive.  I was driving down a steep mountain road and had to stop the car twice to cool the breaks because I could not down shift manually to slow the car.  

Answer
Jason,

Go to your local Cottman transmission shop or your local favorite transmission shop and have them read the codes.  The transmission seems to be attempting to protect itself.  Sounds like a servo to me.  But, from the computer I cannot complete a diagnosis to know for sure...  Email me back with what you discover.