P3000 and decreased mpg

Hello! I have a 2013 Prius v five with 124,800 miles. I purchased in feb 2016 and it got 39 mpg. Then, it hovered around 38, and for the last month it sits at 37.4.

I noticed after I bought it, when I turned it on and began to drive immediately, that the brakes would catch, for lack of better term, about 5 times and then drive normally. But last week, the car was in N going through a car wash, The car made a strange noise and an orange rectangle appeared around the hybrid battery indicator. As soon as possible, I put it in park, turned it off and turned it back on. It lurched and spun out a bit, then went back to normal.

I have also noticed the battery level seems to rise and fall what seems like quickly to me, but I will gladly admit I don't exactly know what to look for or what's considered normal.

I took it to the hybrid specialist at my mechanic and he showed a P 3000 code with a sensor issue, where the car registers -40 degrees as if I lived in Antarctica, but I live in Tennessee and it feels like the surface of the sun right now.
They recommended a four hybrid system replacement, at $3500, and also that I ask Toyota consumer affairs for a goodwill battery replacement since it's so new. Toyota insisted I have it reevaluated by a Toyota certified mechanic. The Toyota mechanic found the same code, cleared it, kept it overnight, and ran test drive it twice to see if they could replicate the problem. They said it could have happened if the car ran out of fuel, which it didn't, or if it was left in neutral for too long, which has never happened beyond a 3 min car wash. Ultimately, the Toyota dealership did not recommend any repairs at this time.

What do you guys think?

 

Good to know! Thanks!