Fuel "efficiancy" is a thorney issue at best, getting the best from any i/c engine has many facets, not just those asociated with combustion. there is the question of mass/power ratio, friction elements, braking etc; come into the equation.
One element is driver anticipation, slowing by deceleration not brake use?. Yet the "modern" teaching has students, "braking to a stop". I look to continue progress, lift off and if clear, into the turn without a stop. Matching the "economic" RPM to road speed via the gear ratios in use at any given time, something not always possible with automatic gearboxes.
Pete.