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Upon further checking, it looks like the MSDS I pulled from AC Delco's website was for the wrong product, but it doesn't change my previous conclusions or the remaining questions.
It looks like the current OEM product used in our TR6060 (AC Delco #88861800), which Summit Racing lists as meeting the GM OEM spec 9986252 (the same spec as the 2013 spec sheet that UnknownJinx attached above in the thread) is now a 75W/90 oil. I looked on AC Delco's online catalog and found product #88861800. While they don't have a spec sheet or MSDS for this product, their summary info for this product says:
"ACDelco 75W-90 Manual Transmission and Transfer Case Fluid helps improve fuel efficiency, reduce operating temperature, and improve thermal stability. Gear oil adds lubrication designed to help reduce heat generating friction caused by gear components while also helping provide corrosion protection."
Based on the trans oil weight for the Tremec product (75W85), and Matthew's note above about RL D4ATF being a 70W80, it certainly looks to me like the current GM OEM trans fluid (AC Delco #88861800) is no longer the Dexron III ATF like it used to be and is now more viscous.
So, why did GM start using a thicker fluid than ATF Dexron III in the TR6060, especially when the TR6060 calls for Dexron III ATF?
If we are willing to assume that it's more appropriate to use the OEM 75W90 fluid or the Tremec 75W85 fluid, is the Tremec fluid any better than the OEM? Is is worth 2x the cost?
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