HELP having issues on bank 2 lean

GuiLLoZ

had a p300 missfire then a 302 which is cilinder 2 i replaced de coil and problem solved (not quite) currently i went to retune my car with ecutek. the tuner said the bank 2 was leaner he was giving the same % of gas and the bank 2 didn't responded stayed on 13.5 and the bank 1 was on 11.8.

He then loaded a map for turbo with the speed density to see if the mafs where the problem. Nope still bank 2 lean, then he said check your o2 sensors they are reading different voltage even 1 volt difference which he pulled other 370z logs and the o2 where slightly parallel to one another. i am planning on changing again my o2 sensors. He tuned individually bank 2 making it richer to maybe even the odds until i change my o2 sensors and try again.

My question is: is there something else causing this? voltage and the bank 2 be leanner other than the o2 sensor, don't want to think it is an injector problem in cruise he performs great, even thou my mpg are 13.8 which before was 15.4. Maybe a vacuum leak? but for now i am and if this keeps up maybe sell the car.

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Stillen gen 3 CAI/koyorad oilcooler/custom full exhaust/ecutek/20mm spacers/megan springs