I have a 2013 WRX with a Cobb SF Intake and the 93 Octane Cobb Stage 1 + Intake HWG map. After installing the intake and flashing the new map, the average gas mileage for my daily commute has dropped from about 23mpg to 18mpg (tracked over a period of ~2 months on both sides of the install). For reference, I commute from Somerville, MA to Bedford, MA using route 2, 95, and route 3. So, it's a mix of interstate driving and a little city driving.
This was a much bigger hit to my mpg than I had expected from just a stage 1 map. Does this seem reasonable? Or is it a sign that something could be wrong?