Q: I have a 1990 Chevy SS454 pickup truck with 191,000 miles. It's time to change the transmission fluid again. The information in the manual says to use Dextron II, but the last time I had it changed, the dealer put in Dextron III, which he says is better than Dextron II. The auto parts store said I can use Dextron III fluid for vehicles over 75,000 miles and it will not hurt the transmission.
A: The latest and greatest GM automatic transmission fluid is Dextron VI. Not sure why, but they went from III to VI while skipping IV and V. As with most newly introduced OEM fluids, Dextron VI ATF is improved from Dextron III, and backward compatible. Not that Dextron II or III would harm your transmission, but Dextron VI is now the recommended fluid for all GM automatics that originally used any form of Dextron. We don't see many SS454 trucks on the street. Hold onto that one. Not sure what the auto parts person meant with the 75,000-mile marker, but use a big name brand of Dextron VI on your next transmission service.
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