i have a 05 Dakota 4.7l quad cab 170000km on the clock. the problem i have is bed bounce at higher speeds only on the left such a 100km/h and seems to get worse when accelerating but some times its way less than other times. i put in two new kyb shock absorbers in the back and it did not help at all. the old ones were blown though so i thought that was the cause but nothing. it seems to we worse while going over a bumps. the right side has zero bounce but the left goes nuts. ive picked the bed up at all four corners and no play at all. jumped on it and nothing. the wheels are missing no weights and same with the drive shaft/ no dirt or mud on them. i have no idea.

 

check to see if you have any broken shock mounts, the welds could of cracked

 

Sounds like maybe a tire out of round.

 

Can't hurt to have the rear tires rebalanced by a reputable shop. Do you get a howling sound when at highway speeds?