Update.. 4Lo working
I'm both lucky and an idiot...read below.
The codes, C1234 (I think) Open Center Diff and the Zero Point caused the motor to shut off after starting.
I needed to get back to just the clunk so-
Attempted to run the Zero Point calibration. Would not stick.
Unplugged the actuator, turned the truck on, then off. (remember I think I caused this odd combination of codes when I unplugged the actuator WHILE the truck was running)
Plugged the actuator back in.
TRuck on, code for Open Center Diff gone. Now only Zero point remained.
Ran the calibration, code gone!
Truck runs and drives, Center Diff engages and disengages properly.
Loosened the bolts holding the actuator to allow for maybe a millimeter of separation from the housing and the TC.
Rattled it a bit by hand.
Started truck, put it in Neutral. Attempted to engage 4Lo. No love.
Decided to check the switch.
Pulled the center dash section off so I can get to the plug.
Jumpered the plug from the back, 4Lo ENGAGED!
Jumpered it back to 4Lo off.
Decided to pull the switch. As I was trying to get it out, realized the plastic knob had a crack in the mated part so it would no properly turn the switch.
That was it.
4Lo works great.
I plan on boroscoping via the fill hole this week.
I'll report back.
Yes, I know I'm going to end up buying a TC but it's good to know the actuator works.