Yours truly FINALLY got the brake controller working and the trailer to the service place today.
As an licensed, registered professional engineer I am honest in my data driven evaluations even when evaluating myself and I have to say that I am no electrician.
Oh I can whip up a cheesecake and feed 17 people a thanksgiving dinner out of my popup at the Fort.
Microsoft Excel pivot tables are putty in my hands.
Physics, astronomy, and calculus are like falling off a log.
But give me a wiring diagram and a bundle of wires in a confined space and butt crimp connectors with a
YouTube video of my exact situation and you would THINK that ol' Eddie could pull it off.
And I did. Barely.
One broken drill bit, some skinned knuckles, and a few choice words uttered in the safe enclosure of my vehicle later, the little Prodigy P2 controller blinked "nc." (no [trailer] connection) when I powered it up. Praise the Lord.!

It was time to now hitch up the trailer and check the drop/tow level.
I think the 8 inch drop I got (allowing for some rear sag) works fine.
Just before leaving I threw my level on it and the bubble is acceptable.
Then I towed it to the service place and took the longer way around so I could take it up on the interstate for a short run at highway speed. My first impression is that GMC at highway speed barely acts like it knows the trailer is there. Now I was by myself in the vehicle with no gear in the rear but it felt a little stronger. The SUV as a whole rides a little taller and firmer than the Chevy did. So I don't know to what extent the 3.42 rear axle makes a different versus the old 3.08. Or if it's the changes that took place in GM on the big SUV redesign in 2007. I'll be curious to see what kind of gas mileage I get on the first tank towing to Cocoa Beach in a few weeks.
Thanks to all of you for your advice and looking over my shoulder with suggestions.
Bama Ed
PS - ol' Eddie can't hit the curveball either ......
PPS - and the work being done at the service place? Wiring .....
PPPS - tiggerdad, that green apartment building under construction over my car on the street now blocks the view of Bryant Denny Stadium (Alabama football's home on gameday) that I once had and it makes me

. I'm gonna have to call the Mayor!