I would start first by removing the rear wheels and turning the drums by hand to see if the brakes are dragging. If they do not seem to be, then I would just adjust both rear brakes again. With the rear tires off, remove that rubber grommet from the drum and use a brake tool or flathead to tighten the brake "struts" (term maybe incorrect) until you just cannot rotate the drum by hand and then back them off four or five clicks. Do the same thing on both sides and see if that helps.
As for the parking/hand/emergency brake... you have to remove the center console to gain access to the cable to make the adjustments. Hope that helps.

I forgot... inspect the drums and shoes while you are at it, that may also be part of the problem.