2nd Gen Non-Engine/Transmission Trans temp gauge

[HTRDHLR]

I have had the Nordskog digital trans temp gauge in my truck for about 6 months. It worked fine mostly running about 165 and would drop fast as soon as the converter locked up. Now it seeems very high (215) and does not drop like it used to. I even noticed it jump from 185 to 200. It never used to do that. Any suggestions?? I suspect the gauge not the trans

 

[Cooker]

Sounds like it may be a bad sending unit.