I think downshifting in D reduces the range of gears available, as Cabinetman observed. I haven't tried this, except by accident. It might be a nice way to counter all the complaints about "too many gears." Drivers could limit the car to 1-4 only by downshifting to 4. I'm gonna try this on the way home today. There's no need for 8 gears on my 35-mph road home.