You mention the AFR but not where it was measured. If it was done via a O2 sensor sitting in 1 tailpipe it's reading would be really different then where the stock 02s are since the cats produce 02 and thus reading at the tailpipe would not be what is really what is seen before the cats.

Airfilter and how it is mounted to MAF would dictate air volume and it's temperature. a good filtering system over stock should increase MAF flow and be cooler in temps.

At WOT if you see around 27 lbs/min and IAT is close to outside temp then it is a good design and since airflow is being increased the AFR for part throttle will get leaner then stock setup and thus if the PCM calibrates to a long term fuel trim (LTFT) close to zero then a performance increase should ocurr.

If LTFT was already lean, then adding a good airfilter system will make it even leaner and then to make use of that better filter you need to install larger injectors, a MAF translator, both or as I do now, do your own PCM code changes to re-calibrate powertrain to properly make use of the cooler increased airflow.

I am not into the $500 airfilter mods, my tests show them no better ( and sometimes worse) then a $250 filter and a true cold air box.