Transmission slipping

Hi, I have an '04 S60 T5 with automatic transmission. Recently the transmission will slip between 2nd and 3rd and ocassionally between 4th and 5th. It does this randomly and not everyday. Has anyone had this problem and know what is causing this? The car is out of warranty. Any help would be appreciated. Thanks

is it overdue for a trans flush old burnt fluid can cause slippage internal wear and damage