I'm a tad disappointed with my mpg - OnStar says 35 lifetime but calculated out is 34mpg - right with what the combined mpg is supposed to be but I drive 80% hwy miles. I stick to 65mph most of the time but do drive 70 on occasion. I try and drive to creep the mpg avg up but it seems finicky.
I'm almost set to blame the lack of quality gas stations - don't have many that have separate lines for 93 (87, 89 and 93 combined into one) so I do get a mix of 87 in there.
It's silly though, when I fill up with 93 the miles remaining always says "430". When I fill up with 87 it's "395" so the car knows what octane I'm running yet I still have problems getting the mpg to be 37 on the hwy, even with 93 @ 65mph.
Still stock here on my 1.4T and 3500 miles on factory oil and air filter. Guess it's time for full synth and K&N filter.