[RIP]

Far from a tranny expert but all I can see left to do short of getting yet another tranny is get it flushed, maybe twice. I don't normally recommend it but in your case I can't see it hurting.

As I've read, reputable tranny shops (they do exist), when presented with a tranny showing catastrophic failure (debrie in the pan), will automatically change the tranny and the torque converter and at least flush the cooler if not change it. Debrie will hide in the TC and cooler and destroy a new tranny.

Has anyone checked for transmission fault codes? A dedicated tranny scanner is needed. Are all the electrical connections clean and tight? Which transmission are we talking about?