It's the new gas, try adding 2 bucks worth of Diesel to it per ten gallons of gas it seams to help mine out a little, the more they mess with the fuel the worse it gets, try sticking with mobile or chevron gas, I just took a two thousand mile trip and the cheap gas stations turned out to be not so cheap, I started out with 43 mpg and went down as low as 28 mpg with the same rig, same day of driving, same hwy, just diffrent gas stations.