I don't have any experience with Chevys. But I do know for all vehicles, it matters how the exhaust system and intake system were designed as to what mods work well for what vehicles. Some will just add sound and/or bling, sometimes at the cost of performance. Others will add some performance.
For instance I used to do Hondas, and they would respond very well to upgraded intake.
On my E46 BMW though, the intake was very well designed and there wasn't much improvement you could make for it. There were even people on the forums who dyno'd with factory airbox and with an aftermarket intake and had a loss in power with the aftermarket stuff, especially after it got heat soaked.
Some manufacturers make some models with everything lined up very well from factory and aside from aesthetics, you won't gain much there.
There are other manufacturers that throw in the same parts across a bunch of vehicles. It works well for most, but there may be some models that could be improved upon and that's where the mods help.
I know it was common for people with a CB7Accord DX/LX to put on headers, but those with an EX would leave them. This is because the DX/LX had a 4-1 reducer from the manifold to the exhaust and the EX had a 4-2-1 that flowed properly and gave a bit more power. Headers helped those with the DX/LX, but did nothing but add bling for the EX crowd.
So get on a chevy truck forum, see what people have done and what actually works to get more power and/or gas mileage and decide what will work best for you. There is no universal answer that applies to all vehicles.
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