coasting downhill in neutral is far worse than coasting downhill in gear... coasting downhill in neutral is no different than idling your engine in traffic, whereas coasting downhill in gear, the ECU shuts off the fuel injectors until around 1500rpm on most cars

Take most of what you learned from saving gas in a carburetted engine and throw them out the window, because fuel injection is much different... if you want better gas mileage, STAY IN GEAR!