First time using synthetic

First time I use synthetic oil in my Alza. Royal Purple 5W-30 engine oil (API SN rating) and Schaeffer synthetic ATF. Experienced loss of power at first. Checked and found out that the ATF was overfilled. Drained out a bit and now the drive just feel nice. The engine doesn't scream as loud or sharp as before at high rev. Much more subdued. But the autobox still doesn't shift smoothly or at the right time. The colour of the ATF drained out looks quite dark as well. Maybe will do another ATF change after 5000km and see if things will improve.