Hey guys, i got a 2006 nissan xterra s with about 12,000 miles on it, and over the last few week i noiced that my MPG's drop from 16/17 to 13. I changed my driving style to see if i was using my lead foot to much but still the milage is the same. I took it into the dealer and they found nothing wrong with it. I change the oil every 3750 miles like the manual says and do all the other rotine matinence to it, any insight on how to fix this problem would be great.

Thanks