Tahoe check engine light P0171 & P0174

2003 Tahoe 5.3litre 50K
The ses light is on again, dealer reccomended fuel injection cleaning for $120, done that now the problem is back. The only sympton is rough
idle that is not always present.
The codes mean bank 1&2 lean - could this be MAF sensor or 02 any advice is appreciated.
thanks!
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This needs to be closely scanned, any excess o2 in the exhaust stream causes this, poor combustion, egr not seating, lean mixture due to wrong baro readings, engine miss, vacuum leaks and the list goes on.

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Thanks for the info...Found air leak with the intake manifold gasket. Thought they corrected the problem with the gaskets on the newer vortecs ? Guess not.
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