did the tire size thing as that was my 1st guess all good the driveshaft is a bolt onto flange setup pretimed when built (I hope) Am going to change the oil in the transfer case as have read the it can be a problem ,should be done anyways. Have been waiting for something to let loose for 2 years and 20,000 miles and nothing happened yet. Ive talked to a local gm w/a guy and he wished me luck as trying to track the vibration down on higher km units is really tough.