I thought it might be the 1/2 shift too but since the rpm didn't change, I wasn't sure. I guess the car has to be under load. Question. Is the driveshaft jumping normal or is the transmission mount the issue like the first reply said?
A bad transmission mount would cause the front to move with the tail housing.
Mopars were notorious even from the factory for some gear whine. Usually this is the grar setup being off a little. This never seemed to affect reliability.
Watching, I note the yoke as well as the driveshaft jump. Could the pinion nut be loose allowing the pinion to flop around. Try pushing the yoke and driveshaft up and down with no load on the driveshaft, eg in neutral.
