This is pure speculation, to see if anyone else ever felt this.

At highway speeds and above, car likes to wander left, then right, then left, etc. Not much, just barely perceptable, but requiring vigilence to stay pointed straight. Front has been thoroughly gone through, new struts, springs, ball joints, control arm bushings, steering links, wheel bearings, etc., and I cannot detect any freeplay. Steering box has also been adjusted - there's no steering wheel freeplay. All alignment parameters are within tolerance.

Could it be that the non-posi diff is transferring power side to side (left wheel to right wheel) enough to affect the aim of the car???

 

No, there are tens of thousands of non posi rear wheel drive cars on the road without this problem.

 

So then, your theory would be.................???

 

UHH, that the open differential is not the cause????

The real problem , if you want the truth, is the alignment. IF you say everything has been checked or replaced is TRUE.
You need to take it to a well experienced alignment shop. NOT a chain store or ANY shop that hooks it up to a computer and gets the specs out of a database.
You need an alignment done for your cars specs, the way you have it set up, not the generic stock camaro specs.
Especially if you have different tire sizes front to rear or have wide tires, even lamborgini's and ferarri's have problems like this due to the wide tire sizes and the crown built into normal roads.
Sometimes you can't correct this wondering problem because you have to align it to conpensate for the uneven road surface.
You probably just need more caster, and make sure it's not toed out. Should be about 1/8" toe in.