I used to get about 14 mpg. The last few tanks I've gotten about 11. I know that the winter gas blend could affect the milage, but this just starting happening...I think they change the blends around Nov where I live. My tires are up around 35 psi. I've 65,000 miles and have never changed my plugs...the engine runs silky smooth...Could it be the intake gasket...

Any other thoughts on likely sources would be much appreciated.