shifting problem what could be the cause on 2003 Chevrolet Malibu

car shifts fine then at 30 seems slow shifting so guess its slipping.rpms seem to be fine as it will rev up if you drop down to 2 on gear shift it slows down going up hills.i am thinking of buying this car for $650 but not sure what the problem is or how much it will cost to fix.

Asked by for the 2003 Chevrolet Malibu
your symptoms may or may not be transmission related, I suggest having a professional perform a test drive to give you advice on how to proceed,
at that point it will be easier to determine a direction.