Roush Why would my Rear Brake Calipers Keep locking Up??

Ok, Thursday I had my Mechanic Friend Install the Rear 13" Slotted Baer Brake kit on my car so it would match the Front Saleen Alcon Slotted Rotors on the front! (Looks Awesome by the way) But on Thursday I drove the car home and all was good til I got a few miles a way from home and I could hear and smell Brake that horrible Brake Smell from the drivers side rear rotor hitting the Stuck pad/Calipers?? Parked the car, looked at it, talked with my mechanic and went to drive it again 40 minutes later and all was good! Today(Sunday), I was driving the car and then I could hear and smell the same thing on the passenger rear side! Got the car home, left it in my drive way running, parked,had my step son get in it, put it in neutral, take the emergency brake off and I could see where the rear driverside pad disengauged from the rotor but the rear passengerside pad/Calipers were still clamping down on the rotor and still is hitting the rotor and obviously the car was not rolling down my drive way, like it should be! On a side note, My mechanic said this kit was poorly made, in that trying to get the parking brake line to attatch was near impossible and had to be really stretched/pulled on! He was half ready not to put these on because of it! Also, on another side note the car feels like the car lost some of its get up and go power!!! These rotors are heavy and figured it might be that, but maybe the parking brake is still slightly engauged?? Or I have a Caliper problem, Brake line Problem, line Pressure Problem?? Etc... Anyways, I'm driving the car tomorrow back to my mechanic to solve the problem, I hope!! But does anyone have any suggestions, fixs or ideas of what might be going on here??