Transmission Fluid
 

Having to replace shift solenoids - looked at the chart on my phone at Walmart and listed Dexron III - only gallon jug Wal-Mart had was Dexron III/Mercon - afterwards I grabbed a filter kit at Advance Auto and on the sticker holding the lid closed it says recommended fluid Dexron VI. Guess I should return the ATF I purchased? I'm sure it's all backwards compatible?

Use it - it's fine .....

I just bought some Dexron VI and that's what now recommend for our older 4L60E trans If you read the Dexron VI label, it is 'back compatible' for the Dexron III as the Advance Auto label suggested. I don't know what the original GM recommendation was in the Blazer owner's manual. probably Dexron III. I bought a synthetic blend made by Castrol. My problem with any synthetic is it is so hard to 'read' on the dip stick. It is unreadable even in bright light.

I took a look at the Castrol bottle.
 

It says in part, Castrol Dexron VI exceeds Dexron III H requirements. For GM. It is a premium synthetic blend........I am paraphrasing.