I had an automatic 4 wheel drive 2004 Ranger that had bad brakes. I went to back out of my garage about 5 years ago, and I thought that I had something wrong with my transmission because the vehicle wouldn't move. As it turned out, my brakes were locked up. I mention this because I never used the parking brake (A.K.A. emergency brake). Anyway, I had to call for a tow, and the guy pulled me out. A buddie at the time replaced my brakes shortly after, and they were shot. The back brakes that locked up were like sandpaper. There was a known issue at the time for quality problems, but no remedy but replacement. The vehicle had just under 30,000 miles. Never had a problem after that. Not sure of this applies to you or not, but maybe you have to replace the cable since it could be wearing out.

Edit: +1 on BTJONESY's post. If memory serves, that is pretty much what happened to me. The drums wore unevenly or something. I was mad because the vehicle was a lease, and I needed a full brake job. My buddy did the front, and I told him to wait on the back since I didn't want to spend the money. Then, I realized how bad they were, and I had no choice. Either way, a brake job at 30,000 miles is ridiculous for someone that drives mainly highway miles. My 2008 only had pads and rotors done at 43,000, and now at 53,000, I still haven't replaced the drums (they were cleaned off, but are still OEM).