we have the same airbox on my Aurora and your GXP. I gutted it out and noticed a much nicer engine sound. It almost sounds like a turbo. lol. at high RPM'* it has a whistle to it at times.
Stock air box:
It'* pretty restrictive..
My modded airbox:
Below picture shows how I plugged off the airbox resonator.. It made the intake noise much deeper.
aurora with no airbox:
in all gutting out the airbox increased throttle response and passing power. On the 4.6 I am sure it'd be even more of a gain.. It should really liven up your engine! I'd highly recommend it.
I still need to do something with my airbox though to smooth the airflow out a bit. the waffled bottom can't be so great for performance. I don't know what to use to fill it in so I can mold the right shape, and it'd harden when it dries. I'd rather not mess with fiberglass..