I owned a RWD Gt-Line before owning my GT, and when I received the GT, I got kinda scared, the mi/kwh was really low (I use kwh/100km myself).
In the GT-line, normal 70mph driving, I'd get 17-18kwh/100km (3.5 mi/kwh), and when I received the GT, that same exact drive was around 27 (2.3 mi/kwh). I was more worried about the "costs involved" and not really the range as I don't really need 200 miles+. In the UK electricity is now really expensive if you don't get a good deal (over half a dollar per kwh at home).
My GT now done over 1000 miles, and it's finally getting warmer, and I'm getting those numbers back to GT-line level ! I guess it was really just a temperature issue (from 5° celsius to 20).
Done a 120 miles trip last weekend, averaged just under 20kwh/100km, was really impressed.
I'm wondering if there is something to do with "brand new cars", that use more energy ? Or just temperature.