Has there been a change to the type of fuel? When in California they used to switch to "Summer Blend" gasoline I would immediately lose 3-5 MPG due to the lower BTU content of the fuel. I have permenantly lost those 3-5 MPG since the US went to Gasohol, with gasoline having a 10% methanol content requirement thanks to former President of the US George W. Bush and his Congress. If there has been an addition of or increase in the amount of Alcohol in your fuel that may be your culprit, it has been in my case.

Also feel your hubs after a long drive (5miles or more). If one is particularly hot then your brakes might be binding, or the wheel bearings need work.

oxygen sensor they get lazy