2000 Escalade transmission fluid.The truck has been parked for about eight months...now what?

I wanted to know since the truck has been parked for so long...I would very much like to (or better yet have to) change the transmission fluid...how much should I add to the trans.? I'm asking because of the hi/lo 2x2/4x4 four wheel drive option that is in the drivetrain.2000 Escalade transmission fluid.The truck has been parked for about eight months...now what?
The transmission for this truck holds 15 quarts of fluid. The only way to get all the fluid replaced is by doing a flush with a machine. If you do a drain and fill by taking the plug off, you'd be lucky to get 5 quarts out if not less.2000 Escalade transmission fluid.The truck has been parked for about eight months...now what?
Did it all leak out or something???



If it didn't leak out, why would want to add any???



I'm confused??



ADDED:

They sit at the dealers lots for months...All they do is stick a battery in it, start it up and drive away.......

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