This spring I made a discovery that increased by gas mileage from 46 mpg to about 53 mpg. Quite simple. When you accelerate keep your eye on the instantaneous mileage bar. Accelerate slowly enough to keep it at 99 mpg up to about 18 -20 mph. Hard to do past that speed. Then you will be accelerating only on the electric motor. Also when coming down an incline at any speed, momentally take your foot off the accelerator till the bar goes to 99 mpg. Then reapply gas gradually trying to keep it at 99. I think that the gas motor stops when it is at 99 mpg.
I have noted that by doing this the battery charge levels remain lower, which means to me that they are being used more of the time. I am amazed how effective this is. You travel a little slower, but at significantly higher gas mileage.
MarkB