Mine never went to lowest, only low. I don't recall ever reading in the update that it would either. Would have to dig up the release notes for the update that they added Auto, but as I recall both Auto and Conserve only went to low.
That said, mine has been taking a long time to go from standard to low. I'm pretty sure it did it almost immediately when I hit 40 or 45 mph when they released it. I can go up to 2-3 minutes and a few miles at 60 or 70 mph before I see it finally transition to low. When I slow down, it starts going back to standard within seconds. Not sure if anything is wrong or if they want it to delay lowering.
Whenever they did the update that adjusted how often it auto lowers they made this change. I have noticed almost no difference in efficiency and the ride is much better.