[QUOTE=Sentraguy;291154 It is hill country and I can actually hit 45 mpg around town. [/QUOTE]
Wait just a gul dern minute. Hill country? I used to live in Wilson and drove through Goldsboro and Fayetteville regularly. I'm 6' tall and swear I could see right over the top of the biggest hill in that area when standing in the "valley" to the west and looking out onto the water inside the Outer Banks. Ya want hills, drive to Ashville.
It is a little hard to find taller and narrower low rr tires, but the difference in rolling resistance can be pretty large from lowest rr to highest rr: it's a roughly 1:2 ratio. The current Prius tires are fairly wide. The aero vs rr tradeoffs can be complicated.
If you look at a bsfc map for your engine, you
could find that you don't gain a lot from longer effective gearing (whether from gear ratio, taller tires, or a combination.) You probably will, (in fact the probablility is high) but before doing a lot of work, it would be nice to know that you are getting closer to the engine's sweet spot.
It sounds like you are doing
really well if you can get 45 mpg around town.
You'd have to check the final drive ratio of the manual (and the top gear ratio). They can go either way from the auto. The trans swap would be fun to try. I presume you are not doing engine-off p and g now, and the manual would permit you to do so.
Given your long time spent at 55, any additional aero mods would pay relatively big dividends. I'm impressed with how well you are doing already.