I'm looking to put a aFe Power 49-46112-P Performance Exhaust System (5" from def back) and an aFe Power 50-76105 CIA with scoop on my truck. Will this help with my bad mileage? Im currently getting around 12.9 mpg(20%city 80%highway). I have already lifted the tuck 3" in front and 1.5" back. Also put on a set of 35" AT tires. I'm new to the diesel game so any advice would be handy. I also run diesel kleen additive. Love nissan, but looking for a little better mpg.