I had the p0171 and p0174 code too lean just recently on the LS7 MAF I just installed with the PCM for less tune and intake. I cleaned the MAF with MAF cleaner. Disconnected the negative for 15 min and the clocked the tube that the MAF sits in so that the MAF is the same angle as the throttle body. 25 miles and no code since. Might want to give it a try.
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PCM for Less:Tune,"Rob style Cam",.650 springs,160 stat,4'' FWI,plug wires& boots,3wire kit.LS7 MAF,Dorman E-fans,Pacesetter headers and no cat y-pipe,TR6 plugs.HIDextra 6k