no clue what you are trying to fix hereMaybe? I mean I can see the lever on the diff move when the lever in the cab moves. Do the symptoms I described seem like a sticky locker?
at low speeds, they buck, is what it is
is your seat belt on, not hitting seat belt limiter
if at speed its all good, then not the axles
did you remove cable, move lever by hand and drive - eliminate the cable assembly as a thought
I recommend to drive someone else at least - drivetrain is all basically the same
does it feel like clutch slipping\grabbing?