Just did this mod last week. I bought some 4 inch pvc and two 90degree angles and a home heating and air vent. Cut a 5 inch hole in my stock air box and the metal plate that it mounts to. The rest is explained in the pictures. The truck does seem to have more low end take off power and sounds better when it gets reved up.

 

Noticed water in bottom of your air filter housing (pic 2),,might want to add a couple drain holes just incase. Thank you for leaving the factory inlet & not blocking it off!

 

Thanks for the input. That water was from the rain when I was installing it. I've drove in the rain and taken a peek afterwords. I have not found any water in there yet. I also drilled a small hole in the first 90degree bend to help drain.

I just got back from a 500 mile trip. I average 19.6 miles a gallon. 90% highway and I kept it mostly at 65mph. Seems to have help because I had to drive 55 to get those numbers before. Going on another 500 mile trip today so I'll get more data to average out.

 

wow.
4x4 w/3.73's?

 

yes thats right. with 190k miles. My mileage seems to be jumping around. the last trip I was average about 17. I believe it to be the strong winds were against me.

I was curious to see how much air goes through the tube so I stuck a tennis ball in there and drove down the highway. I reached about 70mph max w/ heavy acceleration on the the on-ramp. The whole trip was only 5 minutes. Arrived home and found the tennis ball in the air box.

I was surprised with the result.

 

I just got back from 1200 miles & got right under 18 w/average speed around 75 mph. 5.3,4wd, 3.73s
As for your flow test, im surprised the factory inlet is that restrictive. May just have to build me one of those road vacuums!