All I can think of is some sort of VVT issue or GM did this on purpose in the computer. This RPM range is around where you would be cruising at high speeds in 5th gear. Maybe it's to increase fuel economy at highway speeds?

If you look at all the graphs for CAI, headers, exhausts though every single one of them sees a massive increase at this RPM though. Much larger then anywhere else on the graph pretty much.

I really wish someone with more knowledge on this type of stuff would add to this.

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