Hi,
Looking through the manuals, where I believe the issue may be with the transmission fluid line pressure. Reverse requires the highest amount of pressure to work.
When you check the fluid level, is it really dirty? I'm thinking that when the clutch packs were slipping, it produced a lot of debris in the transmission and now the filter may be partially plugged causing line pressure to be reduced.
If you look at the two pics, I wanted you to see the pressure differences between drive (first gear) and reverse. I highlighted them.
Let me know if you have already removed the transmission pan and replaced the filter and fluid. Here is a link showing in general how it is done.
https://www.2carpros.com/articles/how-to-service-an-automatic-transmission
IF this hasn't been done, I feel it is a good place to start. If the pan is full of clutch material and dirt, the filter may be the issue or there could be a restriction at another point such as the cooler.
Let me know.
Take care,
Joe
See pics below.
Images (Click to make bigger)
Sunday, January 2nd, 2022 AT 8:32 PM