As you have read in here from time to time, I've played around with various intakes on my truck. I've had in order, a home air-aid style intake that I made a box for and used a K&N filter for a 5.7L Vortec engine. It worked better than the UN-modified OEM air box. I then bought a K&N FIPK, it looked better than my home made intake but really didn't perform any better. Then I decided to make a ram-air set up for my OEM air box, it worked better than the FIPK I was using so I kept it and sold the FIPK. I then bought the UPD intake lid and tube for my truck, it seemed to work better but I really didn't test it. I just sold it soly for the intake noise it made under load, similar to the FIPK, that's why I got rid of it also, and that the ram-air worked better. I really expected to lose some performance putting the stock intake tube and air box lid on. Well, after a week with it on, my truck is actually running stronger, my 0-60 times are lower. The only thing I've done to the OEM intake is the ram-air set up and I've blocked off the lower resonation chamber in the intake tube, that's it. The OEM intake is thicker and heavy plastic than either the FIPK or the UPD. That's why it does a better job of controlling intake noise, I believe that's why it also performs better. Being thicker plastic, I believe it's more difficult for engine heat to affect it. The air box with the ram-air stays real cool, I've checked it after I've driven around. On a cool night, it's very cool to the touch. On warmer days, it does heat up but it's not nearly as hot as the surrounding area or the engine. I believe the only restriction in the OEM intake is the air box, you open it up and it'll work nicely. I've done a lot of experimenting on my truck and gone through several intakes and even more mufflers to find what works on my truck. What I've got now, works, period. I just got an AFE filter to test but it's my last hi-flow filter I'm getting. If it works, great, if not, oh well. The Purolator paper filter I'm using works pretty darn good. After reading the air filter test in Hot Rod magazine, the hi-flow filters only produced about 3-4 more hp and tq than the Purolator filter they tested also. They may help squeeze off another .1 seconds off your ET at the track, but that's about it. Well, I'm done and all of this is just my humble opinion and my experiences.
Jim
pics to the ram-air
http://community.webshots.com/album/30727243ATDYPtGZpG