I got a 2010 S hatchback a year ago with 22K miles. I was getting between 29.5 and 30.5mpg up until a month ago when I got a rear brake job (rotors and pads). I immediately saw my mpg fall to 26.5 and am currently just over 25.0. I took it back to the shop where I got the brake job and they said nothing was wrong. I took it to the dealership and they said nothing was wrong. The dealership's explanation was that the high temps outside (95-104deg - I'm in Central Texas) was affecting the turbocharged engine performance causing the loss of mpg. Given the change was so sudden (I check my mpg weekly), I am finding that explanation very suspect. Is the explanation legit or should I push this further?

Thanks for your help!