These are GM diagrams. Inlets at the top, outlets on the bottom. The radiator is the coolest at the bottom near the outlet where the fluid exits the stock cooler.
This diagram does have the lines flipped at the transmission for some reason as I have never seen a GM with the fluid going through the auxiliary cooler first. I will say 95% of the GMs I have worked with have the fluid input at the top of the OE radiator cooler then it feeds the top of the auxiliary cooler if the cooler is mounted sideways.
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My 1999 Tahoe was plumbed like this and the OE cooler line replacements that went on my Express van when I 4L85E swapped it are plumbed the same way. The van did not have an OE auxiliary cooler but I added one to it.
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