To lean?
 

well i hooked up a diagnostic machine to my truck and said it was running to lean.it could be my fuel injectors ,mass air flow sensor or a 02 sensor.how would I know which is the problem?the o2 seems more common then anything
I might just replace it all since it was someone elsew truck and don't know what they changed and didnt.your take?

I had to replace the upper intake gaskets on my dad's 99 OHV to get his check engine light to go out. His codes were showing both banks lean, tried the PCV valve and fuel filter but it was the intake gaskets above and below the fuel rail. If you go to the auto parts store to get them they are called the "pleninum gaskets"