my 2000 silverado has been a little slow to start up latey. check engine light came on today. has a code 0171 and 0174, i looked them up and it's a lean right and left bank. i'm not that great on diagnosing problems so i did what i knew. i changed the fuel filter(was very dirty), cleaned the map sensor screen(just a little dusty), cleaned the throttle body, and washed& dryed the reuseable air filter(very dirty). changed the oil and filter while i was at it. cleared the codes and drove the truck. the check engine light came on again. so now what might it be? i had the fuel pump replaced about 3 months ago.when it was taking a while to start.