What gas octane? Supposedly they need 87 but 89 will work better. I ran my 87 octane tank down a quarter and topped it with 93. Ran a bit better and seemed like mileage improved. Havent had the tank get to empty yet to do the math. But also check your air filter condition and the airbox for anything blocking air flow. Aside from that i dont know. Its a heavy vehicle driving an awd chassis. If i hear of any issues I will add more.I have been having issues with poor gas mileage only getting between 12 and 13 mpg I cleaned all the vacuum lines and the intake line there's no check engine light on. I replaced the spark plugs also! Any suggestions!