Im having an unusual problem with my brakes. every once in awhile the brake pedal gets firm, and it seems like the brakes are dragging. Ive had the pads, rotors, and booster checked, and the fluid has been changed three times, still no solution. I bought a infrared temp gun and the only thing ive found is that the right front and left rear rotors seem to get about twice as hot as the other rotors....any ideas?

by the way its an 05 GSR with 57k miles, I have rotorpros rotors and hawk ceramic pads in the front, not sure whats in the rear.