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Discussion Starter #1 (Edited)
I have a 2006 GMC Sierra with 215, 000 miles. It has a 5.3L with 4L60 (M30) transmission. I essentially want to do a "spill and fill" service to it. Just drop and clean the pan, replace the filter and top off the ATF. I don't know what type of ATF I should replace it with, and didn't have a service history when I bought it. What should I use? Synthetic or conventional? What type should I use Dexron 3 or Dexron 6?
 

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Do NOTuse 3 or 4. The owners manual will tell you what to use. Dex 6 is what you need. Full synthetic should be fine.
 

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Thank you!
GM banned DEXRON III in 2006 .. GM will not approve of this fluid ..Dexron VI is the correct fluid created in 2006-7...
my 2000 silverado I dumped DEXRON III in 2001 ... aircraft engineer told me to use Mobil synthetic DEX/MERC transmission fluid ...my tranny fluid now looks like new fluid .. in 2001 the GM factory DEX III looked nasty only 20K miles on it .. in 2001 DEXRON VI did not exist ..I still use the same tranny fluid because the VI has a different viscosity..the mobil tranny fluid cost is $11 qt.. a bit more than the VI..
 
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