Itsnotaboutthemoney just nailed it. Your use of the battery could account for the bulk of your lower mpg. You indicated you changed psi to the "correct" psi, but not what "correct" means. Door placard is a bare minimum. For high mpg, you'll need more, up toward max sidewall of the tire. The Prius beats everything for mpg on the EPA tests, but to max it out, you need to avoid dipping into the battery. It's counterintuitive, but true. An avid hypermiler can bury a Prius with a manual tranny Civic or similar, using pulse & glide. Prius carries the battery weight around its neck. Be sure to glide most of the time, not coast. I.e., keep on the throttle just enough to make the HSI bar disappear. You may need to pulse faster than you have to date, at least enough to fill the fat portion of the HSI bar. Some use the power portion of the band also. But still not flooring it by any means. Good luck!
"Not supposed to be constantly monitoring the HSI Display." Hmmm. Then how do you respond to this quote? Sounds like you hypermillers want it both ways.
Clarification. ========== Hypermiling is a series of learned reflexes. It's just like flying plane. A pilot may have dozens of instrument/gauges but a trained pilot only use them for a fraction second - most of the pilot's attention is focused on what's outside and how his aircraft is position relation to the outside - because timing is so important - a trained pilot has to learn certain responses/reflexes (e.g. to prevent a plane from stalling). In a similar situation, computer scientist and psychologist found that what gave many of the expert video gamers a winning edge was learned reflexes and that successful training (of London Cab drivers) rewires the brain. To that end, Hypermiling tends to be most effective on a commuting trip/route that a driver does consistently and repeatedly and its less effective when the driver is on an unknown road without a navigator. The HSI is a feedback learning tool but as the driver gains more experience - the driver looks less at his instrument panel and rely more on his/her honed reflexes/skills. The reference to the HSI display is only to validate a correct reflex/skill but once that skill/reflex is acquired it will not be neccessary to look at the HSI display. Heavy traffic makes hypermiling more difficult. It is easier to learn hypermiling when there is not too much traffic on the roads.