Too Lean (P0174 + P0156 and P0161)

Question

1997 - Nissan Pathfinder (2WD, 3.3L engine). Last summer, I replaced my two front oxygen sensors (upstream). Last month, I had a mechanic replace the two oxygen sensors-downstream (Bank 1 & Bank 2), behind the cc. The 'Service Engine Soon' light is still on with codes, P0174 + P0156 and P0161 which does not make sense since the Bank 2-oxygen sensor is brand new. PCV Valve is also new (replaced last summer) + mass air flow sensor has been cleaned and my Pathfinder is running perfectly fine! My Pathfinder needs to pass smog asap. What should I do here?