Lean Codes. Mechanical or Tune related?

[Chevy305]

So I have a 2012 Silverado with a 6.2L, E38 Gen4. It has long tube headers with high flow cats and a 90mm ported throttle body. I had a local shop do the tuning (this was a few years ago and haven't had any problems initially.) I have since swapped in a cold air intake and magnaflow muffler. After doing so I noticed some cold start hesitation but not enough to be concerned with. This past winter I tried installing a catch can but it leaked and threw codes P0174 and P0171. So I tried a bunch of different things to get it fully sealed (and it was) but I still got the codes coming back along with now very rough cold starts. I installed a new PCV tube to set the system back to stock to see if my problems would go away. The MIL stayed away for about 2 months but cold starts were still very rough. Now the codes are back (3 times today the same P0174 and P0171 every time). I looked and my LTFTs are trending in the 20-25 range and the same lean codes are now pending in the background at all times. My tune shouldn't be that far off with just a cold air intake and a muffler since a shop did the tune for the headers, or is it?

So does this sound like a tune issue that reared it's head at the same time I was messing with a catch can?
Or does this sound like a mechanical problem such as leaking intake gaskets or something along those lines?
Also what exactly in the ECM triggers these lean codes?

I'm a tuning noob and any help on this would be greatly appreciated.

[DHC]

Unless the new CAI changed the tube diameter drastically, that would be the only thing that could be the case if it were tune related.
I would be willing to guess there is a vac leak or fuel pressure issue.
Smoke test it and make sure fuel pressure is at spec.

[5ft24]

what did the magnaflow replace? if the airflow increased significantly, then yes, the tune isn't supplying enough fuel and needs redone for the increased airflow.

[Chevy305]

what did the magnaflow replace? if the airflow increased significantly, then yes, the tune isn't supplying enough fuel and needs redone for the increased airflow.

The magnaflow muffler replaced the factory muffler. The magnaflow definitely breathes easier than the factory one.

I'm going to go around and check for vacuum leaks. If I don't find any I'll start retuning the car.

[DHC]

Check fuel pressure as well. Seen too many plugged filters and half dead pumps that people try to "tune" around.

First rule of tuning: Ensure mechanical preparedness before changing tune.
Second rule: Tunes don't go bad, mechanical parts do and with crap tunes they wear out faster.

My opinion.

[Chevy305]

I checked for vacuum leaks with carb cleaner and again with a propane torch and didn't come up with any obvious leaks. Even though they didn't show up with my leak testing, could the intake gaskets be bad? I've been reading about others posting the same question and the answer is usually intake gasket leaking.