If you go to your owners manuel and follow the battery and transmission relearn when battery is changed or disconnected,it will show that the engine must relearn its idle and fuel trim strategy for optimum performance,same goes for the transmission,it must relearn its adaptive strategy ,as a result of this the transmission will shift firmly which is normal,overtime the adaptive learning process will fully update the transmission ti its optimum shift feel,so essentially so many variables are to take into consideration pertaining to driving style which is stored on the ECM,when battery is removed or disconnected all of the data is erased and must later relearn it again.