Thanks Dr Quick,
The GM service manual says that with the HD tow pkg there are 7-wires in the tow harness and there are indeed 7 wires, with exact colors as in the manual, with the only difference between vehicle and spec being that brake signal is not in the two blink/brake wires.
I almost went ahead and wired the brake into the blink wires at the rear yesterday but I wanted to explore further to see where the brake signal was being dropped and if I could correct it properly. I couldn't find in the drawings where the turn signal and brake circuits are ganged or OR'd together and I wonder about possible faulty relay(s) or fuse(s) and I wonder about ganging them at the rear if I might be putting more amps in those small wires than they were designed for (were amps stepped down when the brake+turnsignal circuits were ganged together?).
