I tried building a second intake tube into the fender just behind the original intake tube. In addition I removed the HC filter and installed a drop-in K&N. All of this gave no improvement in quarter mile time and reduced low end torque substantially. The truck could barely squawk the tires after performing this mod. Some airbox mods do work....see Hi_Volt's mod in the Gen 1 threads....but the one I tried on the 5.7 did not. Perhaps another location for the extra hole(s) would work better.
I drilled a 3"diameter hole on the bottom of the box after I installed a K&N drop in filter, I lost some low end torque and I hated the noise it made at WOT. So I filled up the hole and drilled 3 smaller holes(3/4" diameter), the sound's just perfect and my buttdyno tells me it's a great mod.