so since ive owned my truck its always showed 17.7 miles per gallon as my average fuel economy. well it had been slowing dropping so i decided to change oil using mobile one 5w/30. cleaned my air fileter and the mass airflow sensor. havent had a chance to change my fuel filter as its in the tank. After doing all this i figured it would improve alittle but nothing its still dropping. its at 16.5. Its an 05 ecsb 5.3 2wd. I also just started using premium fuel as well. Does anybody have a clue what i need to do?