Poor gas mileage all of the sudden.

Hi folks Mike here. I have a question. So recently I had a battery replacement by the same guy who reconditioned my battery almost two years ago and the car seems to operate well. It accelerates just fine and idles just fine but when I picked it up from him I noticed very poor gas mileage all of the sudden. It has always given me 42 to 45 mpg and right now I have went through about a half of a tank and have only went 110 miles. Normally I would have had 200 miles to a half tank. The system shows an average of 30 mpg which is a major drop in. That being said the car has tossed a p0011 vvt code a few times in the past but all I did was a few oil changes and the code never came back. The car has been well maintained by a single owner in the past and I have changed the oil every 5k myself. The most recent oil change was 1k ago. I thought maybe the vvt circut filter might be clogged up and I purchased one and even the solenoid itself but never installed them because its been a year since the last time the code came up. The other day when I went out to start the car all of the sudden the code came back. I have a torque pro OBDII blue tooth connector and put it on and cleared the code again. I took the time to examine the timing advance while I had the torque pro app monitoring the system and when I step on the gas it shows the timing to advance to 13.5 to 15 degrees depending on the accelerator position which I figure is appropriate (maybe not though). The average Im getting is from about half freeway and half city street driving. What is strange is when I'm driving as soon as I accelerate I can see the mpg drop way down to 10 mpg and I never noticed that in the 40k that I have had the car.It used to drop down to 17 or 20 mpg. I called the guy who reconditioned my battery and jokingly asked him what the hell he did to my car. Of course he said "nothing". then he asked me what type of gas I use. I told him Arco like I always have for the last three years. Now I know I might get flamed for that in this forum but here is the deal. I know that if I had some kind of injector clogging situation it should not idle so smooth. Even if I was using a better techron gas for example the difference would not be that extreme. Maybe 4 or 5 mpg. When I sent him the car I was getting 45 mpg. When I got it back I'm now getting 30 mpg. I do understand that when the battery is replaced it takes a little while for the system to average out the mpg but I believe it should have done that by now. It almost seems like he re calibrated the system to take it easy on his battery and I am now driving a 1.5L car instead of a hybrid. Is this possible? I only see the mpg go up when Im on flat land or obviously going down hill but it really seems like my prius is not working properly around the city where the mpg should be at its best. I'm always light on the pedal 99% of the time. Like I said the car has plenty of power, it idles just fine, it tossed the code a week ago and it has never came back, the oil is clean. Any suggestions from you folks. Should I just change the vvt thimble filter and solenoid since I have them? The little filter I bought from the dealer and the solenoid I bought on ebay (ughh) it was listed as OEM for $29.00 lol but it came in a "made in china" box. It looks real good but I have been hesitant about installing it.

 

Well....quick update. This is really strange. I did the good old refill and divide the amount of miles I had driven by the amount of gallons it took to fill the car back up and the MPG was horrible. 26.5 mpg to be exact. Now here is where it gets odd. I unplugged the 12v for two minutes and plugged it back in thereby resetting the HV system. After a reboot I drove the car for another 217 miles and hit the half tank mark. System now shows 43.9 mpg average. REALLY!!