you can always remove the intake muffler inside this piece of your intake
all it takes is a flat tip screwdriver and some patience, i noticed a difference after.
after this i noticed the intake for my airbox was behind me headlight. I went down to autozone and bought some universal intake duct (basically like a giant bendy straw) and i ran my intake in from the bottom of my bumper. i noticed a difference after this also. my catalytic converter is also gutted and i have a flowsound muffler.
there are some other mods i've heard of that's i'm not entirely sure that work, i'll list them.
zip ties (or fishing weights) to take the slack out of the throttle cable; you can check if there is slack in your throttle cable by pulling the intake off of the throttle body and having a friend (while the truck is off) push the gas to the floor, if the butterfly valve isn't opening all the way then you have slack. there is a picture out there of this, i've seen it but don't remember where.
blocking the EGR valve with a metal plate. (what sense does reintroducing exhaust gasses after the air/fuel mixture has already been determined??)
running higher octane gas and a synthetic motor oil (my truck loves the synthetic)
BONUS- it's entirely up to you but i happen to have the dual-coil packs setup, i went and bought some bosch platinum +4 spark plugs and my highway mpg shot up to 29 mpg (note i have over 191k miles)