I've hit a wall

Been there done that. Complained even louder.
Every year my "MPG ceiling" got higher. Every year I complained that it couldn't get higher.Every year I beat my previous record.

My suggestion: give your Prius another year to break in and give yourself approximately ten months to improve your technique.

 

The only thing that has caused my mileage to go up is time.

If you're pulsing and gliding, if you're timing the stoplights, if you're anticipating traffic patterns, if you're light on the brake and even lighter on the gas, then you're doing all the right things.

My response was not as flippant as it sounds. For three years I wanted better mileage and I wanted it immediately. I wanted the silver bullet. I wanted the secret.
And I feel that I eventually figured it out: there is no silver bullet; no secret. Rather, there's time and patience and experience and trail-and-error and then there's improvement. When I post my 70+ tanks I point out that I've been trying everything I could think of for four years. If you had told me four years ago that I could hit 70 I would have laughed. Then I would have gotten frustrated to no end that I couldn't do it. It's not that I can't do it, it's that I couldn't do it yet.

Here at PriusChat and at CleanMPG I posted threads exactly like the one you've started here: tell me how to improve my mileage. Of course, the experienced guys would give me a world of advice and a whole slew of tips but nothing would work. I had to have been doing something wrong. But it wasn't that I didn't understand or that I wasn't trying, it was that I needed time to try things, experiment and perfect the little things.

Let's take golf, for example. I'm not a golfer but I heard something on an infomercial once: if you normally average three puts per hole and you bring that down to 2, your game will improve by 18 strokes. Heck, if you bring your average down to 2.5 puts per hole you're still going to see a 9 stroke improvement. Just by improving that one aspect.
But now that you know the secret, how does that help you? Information is passive until acted upon. Knowledge is wasted unless put to use. The only way to perfect your golf game and your mileage is to work and practice and perfect the little things.

Next year you will - without realizing it - be better at timing the stoplights on your route by watching the actions of the cars in front of you or timing the group patterns of the oncoming traffic. You will develop a lighter feel for the gas. You will realize that a 6/8 SoC will improve your high-speed cruising and therefore not focus so much on stealthing. But all these things take time and practice.

I don't waste time writing long responses unless I really want to explain something or I'm really passionate about what I'm saying. In this case, it's both. If you're going to get frustrated, this is the right thing to get frustrated about. But don't fret so much that you grow an ulser about it. Tune in the classical station, laugh at the people in their idling cars and be happy that you are more than doubling the average vehicle's MPG.