If it is lifted it is probably just the change in pinion angle finally taking its toll on your u-joints and pinion seal. If you have 33" tires you probably have a lift. If you have a lift your pinion angle is NOT correct. If your pinion angle does not match the angle at the transfer case you will eventually smoke your U-joints and need to rebuild your driveshaft. Buying adjustable lower links will allow you to lengthen your lower links and put the pinion back into the correct angle after lift.