When I bought my truck used a couple years ago it would pull 18mpg about 200 miles on half tank with my regular driving habits. Then seems since fall last year my mpg has dropped to 14-15 range about 180 miles on half tank with same driving habits. Now I've noticed that I've been able to skip the gas pump a few days each week instead of having to go the same day every week. This morning I filled up & to my surprise I pulled 17mpg with the same driving habits. Which I know the summer fuel usually costs more because its susposed to be better, Could that be one reason my mpgs are up & down? Just wondering if anyone else has noticed this in their trucks. Still need to get a tune to get back up in the 19-20 range any suggestions?