From your description you have a suspension lift, not a body lift. First off let me say if you are not competent in repairs or diagnosis of these things take it to a shop to have them have a look. Simply put a failed steering system or part(s) could be a life changing disaster for you and any passengers.
That being said it could be something as simple as a damaged steering stabilizer if there is one on your rig. Old, no fluid,rusted shaft, bent, something like that. Bad/failed ball joint(s) something of that nature. If you are full of fluid and no whining is taking place when you turn the wheel then Id leas toward something not in the power steering system.
