(Another) orange wrench question

[nh39]

Hi all,

I have a 2006 Ford Explorer with over 150K miles. It seems to run fairly smoothly. However, it is showing the orange wrench on the dashboard when it goes faster than 50 MPH. As long as it runs under 50 MPH, the orange wrench never shows up, but seconds after the speedometer goes over the 50-60 MPH range, the orange wrench shows up and remains up for the rest of the drive.
The last time I took it to my trusted shop in the neighborhood, they couldn't detect anything. I did some research online but didn't get any concrete information. Am I looking at a serious transmission problem?
Thank you in advance for your help.

 

[Gadget X]

Might be completely wrong, but I had the same problem on the wife's car a while back. Turned out that the speed sensor was on its way out, and anything over 55 would throw a code. Might be a place to start for you! Good luck with it!