Why would you do something that makes no sense, and will possibly damage the trans.
I believe that trans still has a forward pump which in the old days allowed an automatic to be push started.

A few nights a month I go to the gym late at night and its downhill all the way so I just put it in neutral and cruise. Is that really bad for the transmission with the engine still running?

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2016 Monsoon Gray Audi Allroad - 21k
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2003 Gray Mercedes ML350 - 122k

Used to do long downhill runs in my old Triumph in neutral (Angel Gear) but that was a manual transmission...

Not thinking it is very good for automatics... Besides being illegal in most states...