So I have 2 oil changes on my "new" truck. I run rotella 15w40 in it, mileage went down. replaced both fuel filters twice now. cleaned the air filter and my fuel mileage went from 18.7 to 16.4. I'm not sure what oil the original owner was running in it. I have thought about the synthetics but the 5w40 is,IMO, to thin to use here in AZ during the summer moths when its like 117 outside. I'm also having an injector stiction issue since changing the oil. Anybody else have any similar issues?