Ok so my 2005 Xterra S 4x4 has never gotten great gas mileage. It averaged about 14 mpg and it got slightly worse after adding 33” all terrain tires. That being said I’ve noticed the past several weeks my fuel economy is horrible. I’m getting like 160 miles out of my full 21 gallon tank. That works out to under 8 mpg which is pretty pathetic for a v6 that is driven fairly conservatively. I’ve tried switching to 91 octane, done a fuel system and injector cleaner, tried fuel from shell, chevron, and Texaco same results every time. Anyone have any advice on why my mpg is so poor or advice on how to fix it?