Prius (2004-09) Fuel :: Ridiculous Drop In MPG - Dropped To 43 MPH

I used to get 55-58 MPG when my commute was 65 miles one way, 85% freeway. But these days I noticed that when AC runs hard and trips typically 16 miles, 40 MPH, mpg dropped to 42-45. That worried me a little bit.

Driving style: conservative. I start off normally, but I use N gear as soon as passing speed limit. (this factor alone should enhance mpg by 10 I guess. I used this technique on my 98' Lexus LS400, 4 Ltr V8 engine, once got 38 mpg on freeway, while the sticker says 18/25). This is the main reason I worry that something is wrong with my prius.

Typical range: 16 miles, all local.

Tire pressure: 40 psi

AC runs hard, outside temp 90 degrees, I set temp to 72 inside. (I guess this is the main reason for mpg drop, but I don't think it should drop that much)

I recently changed oil and trans oil.

My battery is a little bit weak, but no warning light. If I forget to turn off head lights, it needs jump in 10 minutes.

Mileage is 143K, 2004 model.

Water pump changed by Toyota free of charge.

Any clue? or it sounds normal and I don't need to worry about it?