Rear Brake Help

you need to elaborate more.

are you pushing on the brake pedal and you can spin the rear tires ?most likely the rear calipers pistons are frozen
are you just in neutral and trying to spin the rear tires?nothing is wrong
is the parking brake applied and you can still spin the rear tires? year pistons are frozen
hard to spin rear tires with the brake lightly applied? can be a slider pins are frozen if they are frozen the caliper is using the inside to push the rotor over till it hits the other side pad and then clamps (you will see alot of inside pad wear and the inside pad will look like new )

I have a 2000 GT and have had to twice have rotors replaced because the caliper seized up on the slider pins, so I'd start there. You can get special grease for those at your auto parts store.