I think I found the root cause, at least...
Searching for some intel on whether there are common issues with this trans, I found this...
" Ford took point on the (10R80) ten-speed gearbox, setting their sights on rear -or- four-wheel drive vehicles equipped with longitudinally mounted engines."
Now wondering, should we continue taking it to the Chebbie Dealer, or just take it straight to FoMoCo?
LOL
One thing is for sure, as of today I'm starting to really like that clunky old, shifts like a wet fart in a bowl of mashed potatoes, 68rfe in the Brodozer!