Good info provided, but what condition was the fluid in when you pulled the pan off last time? If it was burnt smelling or black, you have severe clutches/steels damage from an internal hydraulic leak, causing clutch pistons to engage lower than specs and allowing clutches to slip.
You need to remove a cooler line (from the trans to the cooler) and insert it into a clear jar or jug. Have someone start the car and see if fluid comes out at a decent rate. If so, the pump is working, but the torque converter may have come apart inside, causing no forward/rearward movement. There was a recent thread about a similar problem a few weeks ago. Search my profile and posts, as I commented on them.
Another possibility is that the filter may have come loose, causing no fluid pick-up, unless on an incline, since fluid level, relative to the pickup, is artificially accentuated. Also check the trans filter seal - usually an o-ring.

Good luck, I hope this helps

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Thanks,
Mark in NC

"Spark plugs?...We don't need no stinking spark plugs!"
1985 300SD "Der Silberne Schlitten" 420,000 mi


Wish these were diesel:
2003 Ford Club Wagon 130,000 mi