Truck getting horrible gas mileage
99 Ford Ranger XLT, 4.0, automatic, 4x4.
Im having some issues with finding out what is wrong with my truck. it throws codes 0174 0173 saying bank 1 and 2 running lean. Checked intake gasket, maf sensor and air box and black tube. Nothing. Its getting about 9 mpg or 160 to 180 miles to 16.5 gallons of gas. Ive heard fuel pressure regulator? Vaccum lines behind motor? Cant find the problem and ist driving me nuts. Doesnt have rolling idle or anything idles great. Please Help!!