fuel economy sudden drop I have a 2014 Chevy Silverado 1500 5.3 L V8. My dealership has been great with customer service but is unable to identify the cause for sudden drop in fuel economy. I drive all highway - 175 miles a day, 3 times a week. Starting in September 2016, I started seeing significant drops in MPG. I normally get 21 MPG in summer and 19-20 in winter (I have driven through 2 winters already). Since September 2016 - the fuel economy has dropped and now I get about 14 mpg on the same exact driving routes. It is colder, winter fuel blend, etc. However, I never experienced this kind of poor fuel economy through past winters. I also have family with same truck - and they have maintained their optimal fuel economy. At end of August - I replaced all four tires and lower ball joints. The decrease has been since then. My dealership has helped me troubleshoot: They put on a different set of tires and I drove for a week, no change in fuel economy. We cleaned and replaced the MAF sensor. We are conducting a oil consumption test - with no visible extensive consumption of oil. They have checked fuel trims - no noticeable issues. They have checked tire wear - and no visible signs of poor alignment I am still getting 14mpg at 65 mph on the freeway. Located in St Paul MN