[dudealex1]

All the Buicks that I've driven have always had what felt like a "weak" overdrive... the rpm's just rose 100 or two and then it would fall into drive... Nothing like the crispness of a Honda or Toyota, it's meant to be smooth.

Still, you shouldn't feel a "shake" or "shudder" when it shifts... make sure to check your tranny fluid level with the car running also. The condition of the fluid can tell a lot.

As for accellerating, at low throttle it shouldn't downshift; at medium throttle it'll kick back at about 3000-4000rpm's and then downshift quickly (at least 1000 rpm before redline); at full throttle it should kick back in the lowest gear possible and then shift about 100-200 rpm's before redline to the next lowest gear possible.

Check the fluid level and condition, let us know if there is a vibration/shake or sound when it shifts. And does it slip?