Update: Took it out in the rain to provide some slip, and just going straight forward it still pops left to right. Shifter fix did not take care of this. Arranging to have it jacked up and start yanking at the wheels as described above, but still need to know how to identify my diff ratios, hopefully with no wrenching.

I am still not convinced it is a steering component as the problem would be there in 2hi, operative theory is axle/hub/4wd linkage or something to do with the drivetrain in the front axle.