Have you tried forcing a downshift to a lower gear--to see if it is caused by lugging the engine? That situation happens in 9th gear at approx 60 mph. Caused by the programming of the transmission to get it onto highest gear possible to increase mpg. Haven't previously heard of it at 40-45, but can see where that would be the case at a constant speed. Try forcing the downshift and let us know.
2018 Premier, 2.0T, Cajun Red