GM EVs do not have a locked "base number" for the range. It is a dynamic calculation based on your past driving, current driving, and temperature. One of our Volts said 51 miles on my cellphone and dash however I drove it at 65 mph for 59 miles today and had 0.8 kWh remaining. So the error can go either way. Looking at the phone, it says 54 now. Something interesting though. Road surface and type of weather makes a fairly big difference. That same drive in heavy rain? I ran out of battery at 48 miles at the same air temperature and speed. No wind to speak of, round trip, no heater (only 48°F). The force of the rain and increased rolling resistance hammered the range. But for your specific example, you'd need a second data point. Any other car, EV or ICE, doing the same route, same time. 50% of EPA range is excellent climbing the grade to Flagstaff, or driving down a gravel fireroad. It would be tragically bad on a clear day at 75 mph.