my transmission shifts normal when my car is cold and sluggish when warm. Why? on 2005 Volvo S80

when warm the car shifts sluggish between 2nd and sometimes shifts hard, bucking like I'm rear ended. also when breaking i feel the down shifting, it's a automatic.I had the tranny upgrade and it didn't work

Asked by for the 2005 Volvo S80
seek transmission diagnostic at aamco
Went to best tramission and they said it might be the cyclinder w/o a diaonastic and couldn't get a round about price. Don't want to over pay but stuck. I will call aamco and have them check it out.