Some guy called me today he was concerned about his truck. I asked him what the problem was and he sayed his truck was getting 4mpg. Its a 04 duramax. Can someone help me out here. He sayed he just change the fuel filter about 300 miles ago and the truck runs perfect. He only gets 220 miles to a tank of fuel which is the big 35 gallon tank its a 4 door long bed 4X4 please help.