My 1997 Range Rover just gave off a gear box over heat refer to manual warning.
Speaking how it gave off this same sensor when my battery died I just ignored it.
But it didn't say refer to manual that time.
I've heard of a tube over heating and closing itself. I haven't seen any problems with the tubes so now I'm lost

With this warning coming on intermittently, I wonder if the Temp sensor on your transmission cooler is going bad. If your 97' is like my 00' the transmission cooler should be in front of your radiator. Sensor is #5 on the picture I attached. After looking up the sensor it's not exactly cheap. This is only one of the first ones I found while searching.. It was about half of that on roverparts.com but out of stock. Let me know what happens cause now I'm curious to see what fixes it.

1995-2002 Land Rover Range Rover Automatic Transmission Protection Switch - Transmission - Genuine 95-02 Range Rover Automatic Transmission Protection Switch - 293-01004744 - PartsGeek

My guess would be that the transmission is going out, running hot, and giving you a warning that you don't want to hear. You'll rationalize anything to avoid the concept of a new transmission.

Not sure if a 95 classic and your P38 sensors are the same, but my sensor was going off right after i did a tranny fluid change. In the end I determined that i didn't put enough fluid in."yes it was the temp sensor" Eventually the light flickered out and hasn't came back yet. Maybe its time for a fluid change? I figured that my rover is very particular about its fluid levels.