I've run both Royal Purple or Mobil 1 5w30 since buying my pathfinder new in 2001....130,000 miles and still running strong. I personally like running a quality synthetic product, and also service the differentials, transfer case, and transmission. Don't know why anyone would be against synthetic except for the price. I average 16 mpg city, 18 hwy....tire size, lift, and driving habits will all impact mpg. Short trips and lots of stop and go driving will certainly bring you below the factory EPA rating. I long ago accepted that my pathfinder was never going to be a fuel miser.