Did you swap the wires beween two cylinders like you said? Did the misfire move with the wire or stay on Cyl 5? If it moved, its a bad wire, if it didn't, it's either a bad plug or bad injector/injector harness on Cyl 5 (assuming compression is ok on Cyl 5). Also, did you have the heads checked for cracks and to make sure they weren't warped?