HAve you changed or done anything to the vehicle which may have caused this? been offroad? laneing? Could be a number of things. How bad is the vibration? do you do alot of towing?
Could be: tracking? bend track rod? uneven tyre wear? **** tyres? Swivel pin pre-load? Wheel bearings? CV joints? Transfer box cam worn? propshafts not reassembled correctly? wheels not balanced correctly?
some of those are more likely than others, but its a bit of an open question without eliminating things.
G