99 Malibu tranny probs

My 99 malibu with 118000 miles just started having tranny probs after coming back from my local shop. Now when I shift from park to drive, it slams. Then 1 -2 shift slammed too at first, but now just hits a little hard. Other shifts seems to be smooth, but the P to D really slams hard. Any ideas?

My 99 malibu with 118000 miles just started having tranny probs after coming back from my local shop. Now when I shift from park to drive, it slams. Then 1 -2 shift slammed too at first, but now just hits a little hard. Other shifts seems to be smooth, but the P to D really slams hard. Any ideas?

What was done at the shop? Check to see if the IAT sensor is disconnected, "Intake Air Temp". It should be attached to the hose going from the filter to the throttle body. Being unhook will cause this problem.

New thermostat installed. The IAT is connected.

Wait...... Check the Map sensor and the hose that is connect on the back if the sensor is disconnected then connect it (with the car off) then start the car then check if it stills kicks if this doesn't work well, then check the supports see if they are still good or are they crack or torn if they are that your problem. check all the supports

Thanks, will check that out.