If this vehicle's transmission has bands and further, if they are the type which can be adjusted (not all are), have them adjusted. This should help so long as each band's lining hasn't worn too much. Otherwise, you will be facing a costly repair if the drivetrain is no longer under warranty. Also, every garage in town will tell you they'll need to do a transmission tear down in order to determine the exact cause of the problem, because it's impossible to know for sure what the cause is until the transmission is opened up