When you lift your suspension you alter the angle and the length of your prop-shafts. Lift it too much and you will cause excessive vibrations in the propshafts at road speeds. Also a large lift will cause the UJ's to bind. This can be solved with use of large wider yoke props for the binding and Double Cardan jointed props for the angle induced vibrations. It is often suggested to use the Discovery II front prop as this has a double cardan joint as standard...