B.B to 518 / S.B trans

They did mention the power loss and tried to sell me a GV OD, which I did not want. This car has always run in this configuration so I really have no idea. From what I have read they chalk it up to getting the rotating mass of the OD unit up to speed. I didn't really find any other collaboration to their claim. My car is a street car with 3.91 gears, I drive it everywhere and can cruise at 60-65 MPH @ 2200 rpm... without the OD it would be 3400....