Difference between Dexron III and Dexron III-H?

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I have a '04 Chevy Colorado, 4x4, 3.5L, 5 cyl. base model. The owners manual says to use Dex III for the transmission, (or I'm assuming Dex VI, which is the synthetic.) I have some Amsoil Synthetic Universal ATF that I'd like to use. The Amsoil site states that it can be used to replace Dex III-H. So my ? is what's the difference between III, and III-H, and can I use the Amsoil? Thanks.
 
Great. Thanks. & thanks for the link. It'll work in the tranny, but not in the transfer case......need the synchromesh stuff for that.
 
GM periodically updated the Dexron-III spec. "H" is the latest and last upgrade.

Dexron-VI is not necessarily synthetic. GM's Dexron-VI performance spec is so tough that it can only be met by a synthetic blend or better base oil.
 
Yeah, thanks for pointing that out. I also noticed that when I was looking at the ATF in the store, I saw some Dexron VI that wasn't synthetic.
 
DexronIII(H) had a slighty better additive package than did DexronIII. DexronIII(H) had improved oxidation resistance and an updated friction modifier.

I would recommend GM's Autot-Tract II for the TC.
 
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