The 4T65E transmission at that mileage, often do start acting up.
The hard shifts generally will show/ store a P1811 long shift/ adapt code. (solenoid issue)
In mine, I used a Transgo shift kit into the accumulator once the pan was dropped and it helped to remove the bang/hard shifts.
The valve bodies and solenoids have been known to cause problems, and the heat from transmission can cause varnish build ups.
Adding a half or full can of SeaFoam Trans Tune to the trans fluid may help to ease the shifts and clean valve body etc.
Still nothing in a can is going to fix burnt clutch packs. If the fluid does indeed smell burnt, for reliability, rebuilding with updated valve body & solenoids/ clutch etc is the best option.
Pull the dipstick after driving for 20 minutes+ in park, running on level ground.
Where is the fluid level at full line or? How does it appear nice & red and does it smell burnt?
If you had the trans serviced at dealer, the latest fluid spec is Dexron 6, I hope they used that.
1997 Buick Pk Ave (Soft Ride) Suspension!