This sounds a lot like the rear brakes are dragging.
Basically, that means the brakes are always just slightly on, which causes the brakes to heat, and rapid pad wear.
Note that hydraulic brakes will fail if they get too hot, due to brake fade, so this can become a serious problem.
Checking for brake drag is very easy. Put the transmission in neutral, and jack up the rear wheel so that the wheel can spin freely.. if the brakes are dragging, it will spin less easily, and for less time than is normal.
Since the pads and rotors were replaced, there are a few things that could cause this.
If the caliper pistons were not properly retracted during the pad replacement, the gap between pads may be too narrow for the rotors, this will cause dragging.
If the calipers are not correctly centered on the rotors, this can easily cause one side to drag.