What model are you driving? The 40 kWh? That might be right. You were using full PTC, it was very cold, and were you driving freeway speeds?
My freeway speeds net me around 3.3 miles per kWh. For very cold and running heater / defroster, I would say multiply your normal efficiency by about 65%. So 3.3 times 0.65 = 2.1 miles per kWh.