Bought it used in 2017 w/39000 mi. When taking off from stop, there is a slight (whump) feel & sound as if something is a little loose. Then it is fine… also when coming to a stop sign, there it is again as described above. The driveshaft doesn’t seem to have excessive play in it… ?? What gives?
If you have a two-piece driveshaft, it could be those splines are sticking. Try giving the splined joint a lube maybe. Could be a play in the suspension problem too. When you take off from a stop the front of the car goes up and the rear goes down Visa versa when you come to a stop. Try hand rocking the truck at the four corners, pressing on the bumper.
I am not a mechanic, but what you describe reminds me of several times one of my cars had a broken motor mount.