In my case after replacing both flex discs I noticed the amount of play the rear yolk was showing ,it was around 15 degrees ,not factory specs for sure, try 400k specs ,this could be the issue.I want to pull a yard one but havent found a good donor yet.The more pedal the less clunk mentioned above is correct,the flex disc are a well put design and really help the tranny from alot of abrupt jolts..A high amount of miles on any chassis will eventually give you that lossey goosey ride,clunks included .

Fluid full. Will try some suggestions, very soon.
 

Fluid level fine. Seems to me a vac problem as well.