I know on Toyota truck auomatics the shift control solenoids need to be replaced roughly every 125K-200K miles to fix shifting wiierdness issues. Many owners wrongly assume they need a new transmission when all they need are new solenoids. Transmission does not have to be removed to replace the solenoids.
In your case, since the prior owner replaced the radiator, that is a hint the owner overheated
the motor and probably the transmission