Replacing them wouldn't hurt. Toyota says that the ATF is a long life fluid under normal driving conditions but for peace of mine, you can change the ATF at 80-120,000 miles and every 30-50k miles afterwards. However, I'd recommend doing a drain and fill instead of a flush though. I've drained and filled my ATF every 2 years after I hit 75,000 miles and my transmission shifts fine even with the original transmission filter.