Ok so I read quite a few posts last night from this forum and eventually went back outside to check a few things:

12.2v on the battery as it was (100d outside, about 2hrs after last drive)
13.4v at the jumper post (+) and strut stud adjacent to it (-) when running.
I found an OBC diagnostic thread and found 13.4-6v at idle/revving through the OBC.
I then reset the whole OBC to see if that would do anything. No.

This am, battery was fully charged per my smart charger, started her up, still getting the 4x4, ABS, and Brake lights but the sluggishness is gone: steering feel was back to normal, transmission shifts smoothly through all gears, etc.

Drove into town & got a Starbucks. Back in the truck, no lights are on now & things are peachy. Dropped the wife off at her office and drove to mine: everything's fine.

I think it all started with the 4x4 light coming on once/twice last week & that led to a snowballing of events. Still doesn't explain the "clunk" I felt a nanosecond before the Trans Fail Safe Program flashed on my dash...but if the 4x4 sensor(s) are going that could lead to a wierd setting/shift/power transfer that caused that clunk.

Any input is appreciated. For now I'll look into the "4x4" indicator and what that is & what sensors control that.

Mark

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'06 4.8is Imola Red
'91 911 Turbo
'86 928S Turbo
'82 928 Turbo Race car
'80 Porsche/Glastron Carlson CVX 20 Intimidator,
'74 911 RSR Tube-frame clone Race car