I'm guessing most people who have added performance parts to their engine did it to compensate for things like armor, bigger/heavier tires, etc. I don't really know if you're gonna find anyone on here who bought their truck to buy "go fast" mods to actually make it quicker/faster... I have a cat back exhaust and will add a CAI in the near future, but like I said, it's just to gain some giddy up and gas mileage back from putting mud terrain tires, sliders, a rack, and so forth on it... Just my opinion though.
Aside from cams/turbo/supercharger/tune/gears you really won't notice a measurable difference. I have a custom mangnaflow cat back and K&N CAI. I can't say for certain that it goes faster, but it sure as hell sounds like it and that is what I was really going for. The sound coming from the CAI past 4.5k RPM makes me happy in the pants... truck motors just aren't meant to sound like that...but it does. The part of the exhaust I like the most it the pop and crackle on down shift or when I lift off at certain points. Gas mileage improvements aren't going to be that measurable either.