My 99 CTD with the 5 speed manual recently developed what seems to be a bad vibration in the driveline. It is much worse when the truck is under load ie. towing our 14K 5th wheel. Could it be the carrier bearing on the driveshaft or U-joints. Both I think are original. Truck has 221,000 miles. We are presently setting in a campground in the middle of nowhere Kansas. Any help would be greatly appreciated. Thanks, Dennis

 

Could be. Block the wheels and crawl under and shake it.
Could be many things, but I bet you are right.