A fellow owner was exceedingly ecstatic about their 13++ mpg average on their D.   Unfortunately, they soon realized that their speedometer had not been properly calibrated.   You will have to remove the shroud away from the dashboard to get the back of it where you will find some DIP switches..   The DIP switches are readily seen.   Set: 1 off, 2 on, 3 off, 4 & 5 on, 6 off, 7 & 8 on.   On the small dip switch behind the tachometer, set 1,2,3 off & 4 on.