Yep, sounds like a tall suspension lift was installed without the dealer who sold it telling Stickrpg23 that he would have vibrations unless things were done to prevent that from happening.
What needs to be done to get rid of those vibrations will depend entirely on how tall the supension lift is and what the budget is.
Edit: A simple t-case drop is not enough to get rid of the vibrations a 4" suspension lift causes. You MAY get away with just installing a 1" motor mount lift to get rid of the vibes but that still leaves the driveshaft being marginally too short for that much lift height. For a 4" suspension lift, the correct/best fix is to install a SYE kit and aftermarket CV driveshaft.