I think the higher zinc content, which can be bad for catalytic converters (which Diesels do not have) is why it says for Diesel engines. At the same time, the ZDDP is good for the cam/rocker setup on these cars, anecdotally (I am unsure if anyone has ACTUAL proof but that may require extensive testing on two identical engines leading to destruction, so there's that). Either way, the Rotella will not harm a gas engine that has no cats, such as your 4.5.

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Current:
2021 Charger Scat Pack Widebody "Sinabee"
2018 Durango R/T

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1972 280SE 4.5
2014 Jeep Grand Cherokee Limited "Hefe", 1992 Jeep Cherokee Laredo "Jeepy", 2006 Charger R/T "Hemi"
1999 Chrysler 300M - RIP @ 221k