Codes :"Bank 1 Lean Bank 2 Lean"

[65blackfleetside]

So i have both these 2 codes coming up on My Gen 3 LS . I did a fuel pressure test and it seems to be holding at 55-60 PSI.

Truck runs awesome on start up and at idle. but I do notice a stumble/ motor going lean when I put my foot into it hard. (Its a Drive by Wire)

I did a water test with a pump up sprayer all around the manifold looking for leaks. No leaks surfaced from this test with engine cold and hot.

I spoke to a local guru tuner and he seemed to think its a Mass Air flow
Location issue.

He has not tuned it yet but he explained to me on the phone that he has seen many of these LS swaps run too lean because the location and filtration of the MAF is too close to the intake. The stock location and OEM filter box do not breath as much as the OEM set ups. When you move the MAF to shorter distance- The computer gets confused and needs to be adjusted.

We will see once he plugs in his laptop and does my tune.
Has anyone else experienced this with their LS swap?