35MPG highway on 2014 SW CJAA... bad?

Took the car on a 300 mile round trip, filling up and measuring miles on trip followed by another manual measurement during the fillup.

35mpg @ steady 75mph with 2 people on board. Manual, all 6th gear. This feels suspiciously low and I feel like should be in the 40s even with the dieselgate mods. Car has factory components, 75k miles, dieselgate repairs.