Transmission problem
1999 BMW 528 6 cyl Two Wheel Drive Automatic 158600 miles

I have recently purchased a brand new transmission, a few months later the automatic transmission light came on, and I dont know what i should do, the vehicle runs fine, also I dont know if this is normal or not, but inbetween second and third when it shifts it goes to high rpms then the rpms goes down than shifts, its kinda weird, any suggestions as to what I should do or be worried about.