CAI are a waste of time unless they are mounted in such a way that they breathe in air that isn't heated by the engine. Most of the guys around here add them on, they can hear the engine sucking in the hot air so they think they have an improvement. Keep thinking if you want, that but it isn't true. They are really letting the engine breathe in lower density air due to the air's increased temperature compared to ambient temp. This means less oxygen to aid in the combustion process & less performance.
Most of the hp gains are at the top end of the curve (close to wot), so how long are you wanting to keep your foot in it?
There is an "old school" saying, "there is no replacement for displacement". Still holds true today. There are various ways of increasing displacement - none of them are cheap though
For towing you should focus on low end torque. I would see how it tows in it's current configuration before tossing anything on it. Keep in mind the 4.6 is adequate for lighter towing but the 5.4 is the choice for heavier rigs.
If it was my rig I would make sure I haven't exceeded the towing capacity, freshen up the cooling system and brakes and just go slower.
I've towed @5000lbs with mine and you do notice a difference in performance. I just disable overdrive and accelerate easy. Works fine for me.