2010 Yukon Denali 6L80 Trans Help

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Tanner-

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I have a 2010 GMC Yukon Denali 2WD with the 6L80 with 100k miles. As recommended by the manual I changed the fluid and filter with all ACDelco parts and ACDelco VI full synthetic by dropping the pan, then refilled some and disconnected the oil cooler line and flowed and replaced the rest of the fluid in very small and short increments until the fluid was cherry red. Fluid was dark red but didn’t look to bad and no major burn smell. It’s currently 30 - 40 degrees F outside here and I can’t get the trans warm enough for a hot check. Max temp has been 130 degrees F. At cold fill it’s at the proper level. Now I’m having flare or slip between 2nd and 3rd. And a downshift flair from 4th to 3rd at low operational temperatures. Any advice?
 

swathdiver

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I have a 2010 GMC Yukon Denali 2WD with the 6L80 with 100k miles. As recommended by the manual I changed the fluid and filter with all ACDelco parts and ACDelco VI full synthetic by dropping the pan, then refilled some and disconnected the oil cooler line and flowed and replaced the rest of the fluid in very small and short increments until the fluid was cherry red. Fluid was dark red but didn’t look to bad and no major burn smell. It’s currently 30 - 40 degrees F outside here and I can’t get the trans warm enough for a hot check. Max temp has been 130 degrees F. At cold fill it’s at the proper level. Now I’m having flare or slip between 2nd and 3rd. And a downshift flair from 4th to 3rd at low operational temperatures. Any advice?

Had something similar happen to mine right after the dealer changed the fluid on the drive home. Never returned and transmission has been perfect ever since. If it continues I would run the "Service Fast Learn Adapts" with the Tech-2.

But I'm probably jumping ahead of things, let's do a cold fluid level check, when the fluid is about 80-90 degrees and run the trans through the gears while sitting still and check the level. I live in Florida and rarely get it hot enough to check properly too.
 
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Thanks for the reply. So I did the cold fill test and the level is good. I’ll look into the relearn. That’s new to me.
 
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