Ill try my hypothesis...
The downward pull of the stored tension in the slinky plus gravity is exactly the same as the tension of the slinky thus counteracting the pull of gravity. Once the tension+gravity equalizes to the weight of the slinky alone, the slinky falls at the normal rate of 32 ft.per sec./per sec.
I hope that makes this clearer for you.
If not, well you can say Im full of $hit.
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Thanks, that helped me out a bit.
Just dang!
I wanted to brag about spelling HYPOTHESIS correctly.
Glad I could help though.