Assuming your truck is the one you have in your garage you will have the 4L60E transmission. This is also assuming the transmission in there is still the OEM one. These trucks take a lot of different transmissions, like the 700R4(88-92), turbo 350, 4L65E(2000-2009), 4L80E(93-98 2500 & 3500 Trucks), 4L85E(2000-2009 1500HD, 2500 gas, 3500 gas), and so on. If your truck is a manual, you will have the NV3500 transmission. Your truck, stock, should come with either the 4L60E or the NV3500.
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