Were you loaded down with anything? Elevation? hills? There is alot of factors. I think you should start with getting that chk engine light fixed.. Also i found that not punching it everywhere you go helps out.. Its the driver mod.
I wish I was getting that kind of mileage. I have 5000 miles on my truck mostly City driving and I am getting an average of 16 City and 20 highway. Any suggestions? Been having issues with mt check engine light also.