shuddering when applying brakes

We purchased a 2002 Toyota Pre-Runner last November for our son from a local dealership. By March we experienced shuddering and had to replace both front and back brakes and get new front rotors, even though the previous owner had put on new front brakes only a year earlier. We were told by the service department at this dealership that the back brakes were corroded.

Three months after getting all new brakes and rotors, the shuddering came back. We took it back to the dealership’s service department and they had to replace the front rotors again. They said they think the ones they put on were faulty. Now, even though everything is new again, the dealership’s service department still cannot figure out why its still shuddering in the back end. They said the calipers are fine, but they hadn’t replaced them, and speculate it might be wheel bearings or something else major.

Should I have new calipers put on by a local trusted mechanic before trying anything else more expensive that seems to be based on the dealership’s guess? Any ideas would be greatly appreciated.