It's very likely the brake calipers. The only other thing I could think of would be severely warped rotors, but if it were the rotars that were warped that bad, you'd feel a rather severe pulsing when you applied the brake at anything over 20 mph.

1977 CJ-7, fiberglass body, AMC 360 w/ headers, DUI ignition, Edelbrock intake and Holley 4150 carb, TF999, Dana 300, 4.56 gears lockers, York air comp, 4" susp lift, 2" body lift, BFG 35" M-T tires, Megashifter, AGR pump & box, REP8000 winch.