2014 Prius sudden mileage drop and quickly gets into power mode acceleration leaving eco and ev

I'd suspect a vacuum leak - for the whistling sound from the hood when the car is raised on parking mode.
not sure I understand that description, but if I did get the jist of it, I'd suggest taking a spray bottle of water with a teaspoon of dish soap and spray lightly on the rubber hoses to help find leaks if there are any.

About the reduced city driving mileage, the hybrid computers adjust to the way the car is driven. If you have to continuously make fast acceleration to keep up with traffic flow in S Tex or anywhere for that matter, the car is possibly adjusting to it's drive cycles / trips / commutes. however you'd describe it. If my guess is close, I'd recommend trying to find a way to avoid heavy traffic for a few days at minimum and find a more relaxed pace to see if that helps the car re-adjust to more efficient use of the battery.

Of course if there is a vacuum leak under the hood, that might be the reason for the battery not appearing to be working, or at least might be contributing to the problem.
I can't think of any reason why a vacuum leak under the hood would make the battery appear to not be working right, but I also don't want to rule out any possibilities.

Depending on what kind of hissing / whistling sound it is, it could also be the cooling system, check your coolant level and look for dripping coolant.

 

maybe your hybrid battery going south. how many miles on her?