High temp is one cause for a flashing light. If you can measure the temp with a touchless temp probe while it is flashing, you might see if the temp is too high, if the sensor is bad or not. You can shoot the bottom of the tranny pan and get a pretty accurate trans fluid temp that way.
Could be that your trans cooler is plugged up, or the thermostat on the trans cooler is frozen shut. Normal is around 180 degrees, mine takes a good 10 miles to get up that high unless it's super hot out.

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