This sounds like it has to be something basic. Now if the cooler line was clogged, that might also prevent you from getting a complete fill, right? How many quarts did you need, full is somewhere around 9 right? How about the vacuum modulator, I don't know if it could cause that much slippage, but worth a check. I think pulling the vacuum hose results in no modulation (hard shifting).

__________________
Prost!