Since I found this forum while searching for info on the same problem originally posted here that my girlfriend's '95 Lumina was having I thought I might leave a note on what I found in our case. (Keep in mind that I know nothing about transmissions.)
I took off the pan to replace the filter as was suggested here. I found that one of the three hard lines (bent tubing) had become loose and was no longer secured into its port. I went ahead and replaced the filter and tapped the line back into its port with a rubber mallet. All is fine now.
Thanks you to everyone who write all the knowledgable posts!
;Patrick