I have a 2009 LS460 AWD. It has the eight speed transmission. When the car is coasting, around 38-40 mph the transmission down shifts,enough to feel it, and resumes coasting at about 20 mph. Usually it slows down so much you have to give it some gas. Is this normal for the eight speed transmission? I am use to a 2009 GS350, and a 2004 LS430, which are booth six speed. Dealer checked for codes and found none.