i had an 06 dodge 2500 dsl 4x4 with a vibration starting soft from 80 and right ignorant from 114kms-122kms, dealer replaced rear ujoint on rear driveshaft, and right outer on the front axle shaft. we replaced left front, and the shaft had been balanced during the diagnostic. we also road force balanced the tires to see if there was a shifted belt, nothing. we gave it to the shooter diagnostic tech at a different dodge dealer that the first and about a week later he said he pull the rear driveshaft and drove it on the front drive components and it went away, so he gave it back and said the rear driveshaft was coming apart internaly; one of those foam filled ones.
i would reccomend to you to check first for a shifted belt in the tires and then ether drive it without the rear driveshaft (not too hard though) and see if it disappears.
07 FX4 Level II Ranger
Locked/Lifted/Tuned, and some other toys
89 Bronco II
Rust in Pieces