I was going to put a CAI on my truck, but after reading about 20 or so posts, I'm not sure if I want to. It seems that true gain from a CAI system is rare. Anybody have any hard evidence to prove otherwise? Personally, I don't know much about them, I'm just going off of what I've read. I have true duals, 5.4L, and I'm running 275 65's. I heard the Airraid intake makes a pretty awesome whistle, and that's kinda what I'm going for. Any ideas?

 

The gains are real. I put on the AF1 3" and the throttle response over stock is very noticeable. No more of that lag between puttin' your foot down and the truck jumping. I haven't noticed any improvement in mileage.
As far as wanting an intake to whistle, I'd reconsider that. Some here have had whistling intakes and it gets really aggravating really fast.
Mine gives off a very slight whistle if I punch it from a stop, lasts about a second, if that. After that there's just a nice sweet roar of air being sucked in. That's the sound you're looking for.

Also, if you decide to go with any CAI make sure you don't get one that will cause a lean condition with your engine (unless you have tunes installed to correct for such).

I bought mine from Troyer, they say a 14hp gain. I've never had my truck on a dyno so I can't verify that, but it does make a difference that I can feel.