After thinking a bit I have come to the conclusion that your front drive only experiment means moot. And here is why...
When in 4hi the front end was getting 20% power...obvouosly not enough to pull the VX. All wheels would have been turning equally at the same rate.
In 4lo there should not be any jerking since in 4lo the transfer case is mechanically split 50/50 and takes TOD out of the equation.