The intake will give the motor a deeper, throatier, more aggressive sound, and with an exhaust installed, the sound only gets better. I just started running an Airaid Modular Intake tube with a the stock air box & a K&N drop in filter. The intake is a little throatier than stock up to around 2500-2800, but when you push over 3000 it starts sounding reel good and open. From what I gather, when you add a cone filter into the mix, then the reel deep intake/motor sound is there.
As far as saving fuel....accelerate & decelerate slowly & smoothly. Don't go over 2200 rpm while accelerating. Drive at the speed limit, and use cruise control when you can. Keep your tires inflated from 35-38 psi. (you might not be saving on gas though, if you like to hear and feel your trucks performance... that's my problem ...... The 2008 4.7L sounds really good when it's breathing & exhausting like it should be!).
With my current intake set up & SI/DO XLerator dual exhaust, tires at 38 psi, I can get about 15 mpg city, 22 Hwy, which averages about 18.5 mpg each tank of gas.