I think the GM truck intakes have been pretty decent for a few years now. I can visually see the 04's in my mind and what they look like. If I remember right, they have a large tomor looking resonator in the tube somewhere dont they?
If you're gonna do it, I personally would stick with a handful of brands. AFE, S&B, Volant, or Banks. We all know which one is the most expensive. S&B seems to be the cheapest. Banks uses S&B filters in case you didn't know.
You want something with a sealed air box. Those open filtered intakes are garbage in my opinion. It's defeating the whole purpose of "cold air." Many people have done studies on this stuff, not just the filtration, but the temp of the incoming air. Too hot and it's leaning out your motorThese engiens, like cool, dense air and most if not all intakes tend to heat soak with a motor that's been running for a while, especially if you've been flogging it.
No air filter that's open is gonna be a cold air intake. Sure, it may flow better but it's sucking in some hot ass air. Manufacturers are designing these systems with completely closed off air boxes that feed from behind the headlights or fender well for a reason. And the reason is simple. It's not hot, underhood air.
Amsoil makes a really good, high flowing dry filter drop in replacement. I would look into a cheaper method at modding your stock air box. Maybe try to replace the elbow tube so that it's a smooth flow, without a resonator or the usual ribbing material. That link above looks good. That in conjunction with an Amsoil drop in filter and you got a free flowing, excellent filtering intake. Look at the cost though. Thats a lot of coin just for a molded plastic tube. Between that and the filte,r you've just spend $200. Spend another 40 and you got one of the better intakes out on the marker.
For the Duramax trucks, they make a really nice intake and I really liked mine. The box was completely sealed off from the underhood air and only fed through a small hole in the bottom fo the box and mostly through the fender well. But for the gassers, specifically, your 5.3, I'm not sure what they look like. For the money, they're your best bet.
By the way, I don't sell nor am I endorsed with S&B. I'm just telling you my personal preference. I did look at those for my Challenger 5.7 but opted to stay stock.
If I had your truck and was looking for an intake, I would get an S&B, provided that it's a sealed box.