1989 cutlass ciera has hard shift from park to reverse. Any idea what to replace or fix?

The tranny slams really hard, almost as if the idle is way high but its not. Also when in drive and getting up to speed is fine but comming to a stop the down shift reallyhits hard too. If i drive in 2nd the hard down shift goes away. Any ideas of what needs to be done to fix? i am a mechanic and i am good at remove and replaceing but i am still learning the troubleshooting part, especially tranny issues.thanks.