Chrs987

Hi all! Just got my first Subaru it is a 2009 Subaru Impreza Outback Sport that I recently picked up. So far it has been going great but I will notice something and can't figure out what exactly is wrong or if there is a problem to begin with. When driving I will step on the gas to accelerate and get up to 30-mph the Tachometer will rev up to about 2500-3000 until i get up to speed if I let off the gas pedal it will immediately drop down to 1000 rpm then back on the gas and back up. Just wondering what is wrong if their is a problem I will be getting the transmission fluid swapped soon as well if that will help. It is an automatic transmission as well. Thanks ahead of time everyone!!