Totally a hypothetical question ;)

gtsdude said

throw trans in neutral while car warms up, the torque convert drains when parked and the pump doesn't move much fluid in park, but does in neutral

Click to expand...

That is the issue I was speaking to. if you don't do as you posted, at least my and a few others' transmissions slip in reverse. Perhaps the OP when he posted that his seemed to be slipping in reverse has this issue and nothing more.

just a thought.