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What year did the LQ4/LQ9 become Gen IV?
Neither did. The LQ4 (1999–2008) and LQ9 (2002–2007) are both Gen III, 24x engines. GM's Gen IV iron-block 6.0 truck engines are the LY6 (2007–2013) and L96 (2010–2020), which use rectangle-port heads and VVT. The Gen III and Gen IV trucks overlap around 2007–2008, so confirm with the RPO sticker and VIN rather than the model year.
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