It is either the diff mount, or more likely the beam bushes, very very likely to be these.
Very easy to change not too expensive and make a big difference.
A worn diff will not give you juddering just pulling away, beam bushes will all the time.
You can either fit poly, SUPERFLEX are ace 01749 678152, or you could fit escort cossie one with a GGR axle tightening kit, which work even better, but not cheap.
tabetha