It just varies a lot with my driving too.. I was having a more spirited gas tank and only got 24.5.. This was still my usual 50/50 the same where I got 31 MPG and 30.5.. I notice that the mileage suffers once you go over 65 @ cruise on the highway.. due to the obnoxious gearing I am sure.. 3K @ 70 means gas mileage is gonna go downhill from there..
Normal driving would consist of 45 MPH in 5th gear which sits around 2,400, If I remember right..
Then I would get on the highway at 75 MPH in 6th gear which sits around 3,300.. correct me if I am wrong.
To get 30 I have to go the speed limit in town, keep the revs under 2,800 (this means a lot of shifting

) and then try to be around 55-65 on freeways and highways.