The correct answer to this open question is the following.
The Texas ecoregion that experiences that largest change in temperature in a day was the Texas Panhandle.
This region in the state of Texas has its northern limits with the state of Oklahoma. It is a region extremely hot and to make things worse, it is full of dust, which means it is very dry. Although the average high temperatures in this region are 70 degrees, the Panhandle reached extremely hot temperatures of 95 degrees from 2010 to 2012. These temperatures make the Panhandle one of the hottest regions in the United States.