Start with the obvious, you are running in 2wd rear drive on the road, 4wd lever in forward position, my Dodge made similar racket when I broke a rear prop yoke?? and had to drive home on the front axle, the transfer box made a hell of a racket. A common cause of juddering on the transmission at low speed is oil on the hanbrake band, causing it to grab on, have you checked that? Are all the prop shafts in good order, drive flanges tight, uj's and slipjoints ok, are the uj's aligned on the short shaft between g.box and transfer, have you tried running with front prop removed? to see if has any effect