I think you should read up on some prius mods like one to fool the temp sensor so the car cuts off sooner in the warming cycle, adding a switch for ev mode to use the power stored from the down grade and playing with speed limits.
The prius electric drivetrain is best for coasting and recharging the battery. The gas motor is best for accelerating.
Otherwise do all the other eco stuff, block grill, fully inflate tires and such.
