Thanks for your question!
Have you checked the fluid level and condition in the trans?
Has any work been done to the vehicle lately?
The dipstick will be on the passengers side of engine close to the firewall.
Checking the fluid level is very important.
Also check at the throttle body for a broken grommet for the trans TV cable. You should have 3 cables going to the TB. The accelerator cable, the cruise cable if you have cruise control, and the trans cable. There is a little grommet that will deteriate on thes older vehicles and will cause shifting concerns if this falls off. If it is missing or bad, replace the grommet.