In most of the shots of the car-chase at the beginning of the episode, the General is correctly shown without its side-view mirror, yet in the several-seconds-long clip of the General speeding in from the far distance and whizzing past the camera, the shiny silver side-view mirror is clearly visible.
For safety and convenience, most handcuffs are keyed the same, so even with "new improved" handcuffs, Roscoe would not have "needed the key" to the new sample cuffs to free Cletus; he could simply have used the keys to his own or Cletus's precinct-issued cuffs.
The truth serum that Boss gets shot full of would not force him to randomly tell the truth, rather he would only respond truthfully to direct questions asked of him.