Check engine code: 4th gear incorrect ratio?

[bringles]

I had my 1999 Outback scanned for a check engine code. It has an automatic and 159k. The code came back as "4th gear incorrect ratio" or something to like that. The Subaru repair shop had never even seen something like that before.

 

When I am driving the car 4th gear is fine as are all the other gears. It shifts smooth. What it does do is act like its in neutral after driving for more than 20 minutes. Once it cools down its fine again. Any thoughts on what this could be?

[John M]

That means slipping, and the computer knows that the rpms are too high for the gear you're in. Time to rebuild the transmission.