Transmission error code and limp mode

I have a 2005 Ford Freestyle, 140k miles, with the CVT. Lately, only when driving on the interstate, a transmission warning pops up and the car goes into limp mode. The code indicates that the transmission fluid is to hot. I have taken it to multiple mechanics and no one seems to want to deal with it since it is a CVT. I have, however, received 2 possibilities. A sensor in the transmission, or the transmission is slipping.

I have not noticed any sort of slipping. I have had a transmission go bad before and I know what it feels like it. As I said, this also only happens at highway speeds, mostly during the summer. I have attempted cleaning the fins between the various coolers but did not want to put to much pressure through them.

How much pressure, scrubbing and water pressure, can I put through the various coolers up front without damaging them? Also, is opening a transmission to replace a sensor as expensive as opening one to do work on it? My understanding is it has to be dropped as the sensor is actually inside the transmission with no other access.

Is it time to weigh it for scrap value?