Fast forward another month.
SUCCESS!
I believe my nightmare may be over.

It all went back to the no communication problem. But an unlikely culprit.

I ended up sending the car to the dealer for an evaluation as a last resort. I got a call that they spent over an hour or so going through the car and couldn't find the issue. They asked if I wanted to spend any more on it and I said another hour, but that's it.

Next call from the dealer? They think they've got it.
Picked it up yesterday and put about 70 miles on it. Excellent. Just like it's supposed to be.

The problem?
How about the power and communication leads that go into the TCM were pulled out within the TCM connector just far enough that they weren't making contact!
I'm not sure how that could have been other than like that since the car came from the factory.
Myself, a few other Volvo friends, the guys from Re-Volv and even the Volvo tech had that connector on and off the TCM multiple times and never noticed anything amiss. The connector is large and has quite a few wires going into it. They're also harnessed together so they all move as one. Damn near impossible to see.

Regardless, it seems to be working now.
I'll use the car for the next week or two to confirm, but things are looking good.

Thanks again for all the help. I'm glad to keep this thing on the road.