My trucks pulling a lean code ??

an intake leak, hose or manifold ... pull extra air into engine.

cheap and easy check.. with engine idling, use WD40 and spray around vacuum hoses and where the intake makes contact with gaskets and heads, and a round the TBI.

the idle speed and pitch will change when the WD40 enters into leak.

These intakes will only leak air right?? how can I check intake ??

Some times a Vacuum leak will cause a lean condition. Bad vacuum line, or upper intake manifold gasket leaking.

its a figment of your imagination GM trucks don't have fault codes

could e dirty o2 sensors. or your tbi is dirty