Rear brake problems on a 95 240sx se

[Bronze MFP]

I've had trouble with the rear brakes ever since I bought the car.First off the drivers side rear inner pad got stuck and wore down prematurly, so that forced me to buy new pads for the rear.I put them on last night and they seemed to work fine. I noticed the rear wheels were a bit warmer than the fronts, but I figured it was just extra heat from me breaking in the new pads. Well today I am driving on the interstate and after I get off at my exit, I notice the faint smell of burning brakes and my brake pedal was getting a little softer. I pull over and look to see both my rear pads smoking and the wheels are very hot to the touch.I used grease everywhere when I put the new pads on, i turned the pistons back into the caliper, and I have a FSM so everything is torqued to spec, what could be wrong???I did notice that the rear pistons were hard as hell to turn when I was screwing them back into the caliper, do I possibly need a rebuld or new calipers all together? Thanks in advance for any help.

-Neil