Success!
I sat under the Blazer and verified the pin-outs to the transmission. When I had the harness modified, they swapped OG/BK and RD/WH. The wires perform correctly in the pins, just the wrong color. I was reading other threads on this transmission, and went through the torque converter lock-up thread here:
http://67-72chevytrucks.com/vboard/s...d.php?t=604032 and discovered to my dismay I had wired the brake switch incorrectly (in my defense, I wired it as I was informed it needed to be from the harness guy, which is backwards)
I changed it around and went for a test run. WOW! What a difference, it has a lot more power and just wants to go. No more funny shifting or banging at slow speeds, it feels like it shifts smoother and more consistently, exceedingly fun to drive!
Also- no more whine at shut-off. A very satisfying day, to say the least.