What works to 'fix' gas mileage drop?

Hello all,
I bought a 2010 Prius II (150,000 miles on it) about two weeks ago. In that time the car has been averaging between 41 and 43 MPG according to the computer, and I calculated 41.3 MPG at my last fill up. I am concerned about the MPGs. I bought a brand new Prius in 2012, it was a III model and '12 year. That car always got 48 highway, and 50 in the city. From what I understand, the 2010 and 2012 models have the same engine and transmission set up and the only difference may be the software. So my questions are; why am I getting 7 to 9 MPG less than my old (newer) 2012 Prius? I have read many other posts where people give all the different suggestions as to what to do to get better mileage, but what actually worked? My checklist of repairs include; check 12v battery, change out spark plugs, just changed air filter, check brakes, oil change (using Mobil 1 full synthetic 0w-20), what else should I check/replace/update?

Thanks for your help, and my responses to cwerdna are posted below

- Have you read This Thread Yet?
Yes
- What fuel economy are you getting and how are you determining fuel economy? (trip computer or manual calculations)
Computer said 42.5, calculator said 41.3
- What fuel economy are you expecting and why?
48, I use to have a 2012 Prius III, drove same route and got around 48 MPG
- What are the approximate outside air temps?
70F to 80F, humidity has not been a factor until this past weekend
- How long are your trips?
30min to an hour
How old is your 12v battery? What is the voltage reading of your 12v battery after sitting over night? (Method Here)
Unsure, I should really test it now that I'm reading this
Have you had your alignment checked? Any pulling or abnormal tire wear?
No on alignment. Slight pull to right, though it could be the road, and there is one mismatched tire on the car.
- How much of it is city vs. highway? Roughly what's the average speed in overall and and of each segment? Is there a lot of stop and go driving?
City driving for 5-10 miles longer stretches under 40 MPH, then 20-30 miles on highway speeds between 60 MPH and 80 MPH
- What's the terrain like of your drives? (e.g. flat, gentle hills, steep hills, etc.)
Where I live is very hilly, some very steep, yes there are hills in Florida Orlando where I work is flat
- What are your tire pressures?
Pressure is 36 all around
- Is your oil overfilled? (i.e. above the full mark on the dipstick)
Oil looks ok, but Im not sure what type
- Make, model, year, engine and transmission of previous car? (e.g. 08 Honda Civic Si 2.0L 4 cylinder, manual transmission) What did you actually get on the same trips/commute? (Please give us actual numbers, not EPA ratings.)
2012 Prius III 1.8L, same trips I would get 48 MPG
- What region/state are you in? (if you haven't set your location)
Live in Clermont, FL where there are a lot of big hills, commute to Orlando which is flat
- How are you trying to drive (e.g. trying to stay in electric only?) and how hard are you braking?
Try to stay in electric mode while in slower driving conditions. Braking normal, slow and easy.
- What modes are you using, if any? "normal", EV, power, eco?
Eco mode only
- Are you "warming up" the ICE (internal combustion engine) by letting it idle after powering on?
No
- Are you driving using D or B mode?
Only use D
- HVAC settings? Are you using the heater, AC, auto mode, etc.? If using auto, what temp is it set to?
AC on auto around 74F
- Are you using the factory tires and wheels? If not, please indicate tire make, model and size (e.g. Goodyear Assurance Fuel Max 185/65R15).
Tires are Bridgestone and one mismatched Cooper Tire (unsure on models), all same size as originals
- If reporting a mileage drop, did anything significant change on your car (e.g. accident, hit a curb or big pothole throwing off alignment, oil change/other maintenance/repairs, changed tires or wheels, etc.) or your commute?
Unknown, recently bought car

 

Thanks everyone for the info!

I attempted to check the battery voltage, however I had a dead battery in my multimeter Hopefully that's not a sign of things to come

The bad tire is in the rear left side now. Another thing I noticed is that the right front inner splash shield/fender shield is missing. In the 4 - 5 Prius' I looked at before buying mine, 3 of them had missing inner splash shields. Is this a common problem? I thought maybe my one tire that is different got a bad flat on the highway and destroyed the splash shield which is why its missing. BTW, I don't understand how you get that bad of a flat, I've driven across the country several times, I've been driving for over 15 years, and I have never had a flat!

As for a miniVCI, Bob, it sounds very interesting, but I do not have access to such a thing!