an electrician when troubleshooting a circut always checks the breaker first then the switch then the blub before he starts tearing out the wall...

you should do the same thing....

1. change the fluid and fliter...you would be surprised what symptoms a 20 year old cloged filter will cause...

2. disconnect the vac from the trans... (the vac reduces to cause shift quality) so with no vac it should shift...

3. pull the tranny and have it rebuilt..