You need to do a full rebuild on that unit. The clutches are going to be ruined which is all the black/grey material you found in the fluid. Things that can cause that would be the linkage not adjusted properly. For example if the shifter on the column is reading Drive but the trans is actually partway between drive and neutral it will cause the line pressure to be low and burn clutches etc. Next up would be checking the throttle valve cable which must be properly set its not just a kickdown cable like on a TH350 chevy. If its set too loosely the line pressure will be too low and the trans will slip badly and fry the clutches. I doubt this unit is going to come back from the dead without a full rebuild, but....
1. change fluid and screen
2. Clean valvebody with brake cleaner just hose it all down.
3. Adjust the bands (if they are worn and slipping tightening them up might buy some time providing they have material left on them)
4. Adjust the TV/Throttle cable linkage from carb to trans.
5. PRAY... :-)
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