So how was it possible to remove the EGR systems altogether on the early 2000s engines? Better or more precise tuning/timing? ECUs with a bit more power and/or processing speed?
I'm not even sure if the Gen V engines have EGR systems anymore, do they? It was probably something that at the time worked, but they found a better way to achieve the same without the valve? I think diesels still use EGR (?), but that's another subject.
It was briefly mentioned earlier, but to use F-bodies as an example, the camshaft profile changed on the later 4th gens (and the tune, I'm sure) to reduce lift and duration and increase overlap very, VERY slightly. It had the same effect on NOx as the EGR system, so GM removed it.
Can the same be accomplished on the L31? Absolutely. I just doubt anybody is going to spend the time, effort, and money to run these trucks with different cams and tunes on a dyno with a sniffer to back that up. Even if that were done, it would still be illegal, as nobody is going to go to the further expense of emissions certifying a mod for one of our obsolete engines.
I also find it HILARIOUS that there are so many feathers being rustled over this conversation. I don't see nearly this much interest in the plethora of carburetor/header/full exhaust installation threads that pepper the forums, especially on the environmental tack. If we're going to harass folks for defeating emissions, let's do it with an even hand.