Transmission harsh shifting from 1st to 2nd trans fluid is also very black
You should change the transmission fluid and filter and hope it helps but any damage cannot be reversed without a rebuild.
You can try a product called TransX as a "Band-Aid". Follow the instructions on the can to the letter. I've seen this product work. But as F O R said it's probably time for a rebuild. These GM transmission s are notorious for the shift solenoids failing. They don't particularly like the fluid changed either. But with black fluid it needs changing. But whatever you do, DON'T let anyone flush the transmission fluid. Just change the filter and fluid. No matter what you're told by a repair shop. A fluid flush at this point will be the kiss of death for the transmission for sure!! HTH. -Jim
Lucas transmission fix is another possibility.
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