'98: Going Into Lockup?

Had the thing towed last year.
Tow truck toasted the front diff.
Had the diff fixed at the local Chevy dealer. Almost two grand.
But at that time, all of a sudden it needed a new 4wd switch.... although said switch was working well enough for me to get it out of 4wd after the tow operator had his way with it. I was suspicious at the time - I mean what're the chances of it failing right *then* when the guy was working on the front diff.
Yesterday, my regular guy was checking it over as part of a chassis lube and reported that the plug to the torque converter had been rounded off.... so he couldn't check the fluid without risk of completely ruining the plug.
Now I'm thinking that it's going into 4wd, but not 4-way lockup. When it's in 4-Hi, the steering lacks that special feel that it always had when I'd forget and drive on to pavement on 4wd.
Between the switch and the rounded plug I'm thinking maybe they didn't have their best man on this job. OTOH, the vehicle has almost 170k on it and I don't know for sure that the plug got rounded at the time the work was done - although I would have expected my regular guy (who is the only other one to touch it) would've said something earlier.
Bottom line, how badly could a Chevy dealer mechanic mess this up? Could the lockup thing be something as simple as a wrong connection? I envision a relay somewhere that engages/disengages the locker.

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