I did the airbox mod and it seems to make a small difference on the butt dyno. It could have all been in my head though. I feel unless you start putting throttle bodies, a cam, longtubes, etc., an aftermarket intake will only have marginal gains.
I don't know how true it is the place where i got my tonno cover and steps we were talking about this. He said replacing the filter alone the computer will over ride the add on cause it thinks some thing is wrong, He said do the programer and the filter at the same time. That way you can programe the engine and computer proberly.
I think most of it is just hype. K&n advertises 15.6 horsepower gain for the Hemi , but thats at5600 Rpm.ok but how often are you up around 5600 . So then you will almost never see those Hp gains. You will get a smaller gain in lower rpms but no where near what they advertise.
Stock is CAI...if i want to ^HP then I'll put a SC, torque converter, and tuner on it once the warranty runs out. There is a video on youtube showing these guys in the UK myth busting a CAI. They put a vehicle on a dyno and test it with different CAI set ups vs stock...the only gain they got, and it was very small, was when they actually turned on a fan and ran the CAI by a long hose to the outside of the vehicle...pretty ridiculous if you ask me.