2001 GMC Sonoma P0171 CODE 2001 GMC Sonoma 4.3

MY SERVICE ENGINE SOON LIGHT COMES ON OCCASIONALLY AND HAS STORED THE CODE
P0171. I CAN, T FIND ANY VACUUM LEAKS AND THE VEHICLE HAS MULTIPLE OXYGEN SENSORS. FUEL
ECONOMY SEEMS TO HAVE DECREASED A BIT.
SHOULD I REPLACE THE OXYGEN SENSORS AND IF SO, WHICH ONES? THANK YOU