I have a 2007 V6 limited 2wd 4runner. I was averaging about 16-18mpg with mixed hwy and city driving. One tank of gas would last me about 310miles. Lately, I've noticed that I was only getting about 12-14mpg and getting only 250miles per tank full. I even did a fuel induction service in hoping that it would help. (I should have known better, because it didn't help). I'm not carrying any extra cargo, tires are inflated properly, check engine light NOT on. Drives and performs no differently. I had a mechanic look at it for $100 to do a fuel system check. They found nothing. I had my mechanic change out the spark plugs too. Jeez, i only have 75k miles on it. Any suggestions?