Brake drag. Need help.

10 minute cruise we ran from 60 mph coast and it was about .4-.45 miles to get to 30. That does not sound like brake drag to me.. Thankfully, that tells me that the brakes, lines and such are good. After some more driving, I will check the drag again. It may still be a bad master cylinder. I will check for built up pressure in it whether or not there is any drag. This is just weird as the only thing I changed was to open the master cylinder caps and let out the pressure. The rotors were cool as well.

OR... The master cylinder is getting heated up by the TTI headers cooking the fluid... Would that cause brake drag? Anyone use a heat shield blanket like on a starter?