I dont know it you know the difference in a slip or just a malfunction. If the trans is slipping then yes you do need to replace it but if it just a malfunction then there are some thing you can do to solve the problem but first you have to find out if your car is slipping. Change the fluid and see what happens that is where I would start if I didnt know the difference. Did you check the fluid level from the side of the trans (fill plug). If not then you need to.