I had this identical problem. The only thing that I could do to get the vibration out is true the tire on the rim. The rims are defective and no amount of balancing, or tire replacement is going to correct it.

Tire shops apparently assume that all rims have some amount of imperfections and depend on balancing to correct it. For some reason it could not be corrected on my Dodge Ram. The vibration nearly drove me crazy. Once I trued the tires on the rim, the vibration went away. If you replace tires you have to have them trued on the rim again.

This is not a fix for all vibration problems with the Dodge. My previous complaint will show that I had numerous problems with my Dodge Ram.

I hope this will help.

Before you've tried everything else, this $70 option might fix it.

Problem first noted with about 38K miles on the vehicle and continues with almost 60K miles. At the 40-45MPH range there is a virtical vibration in the rear end as if you're driving over low, closely spaced speedbumps. Once past that speed it stops until about 60MPH but the frequency is faster. So the problem is harmonic relative to speed. The service manager at the dealership has driven the truck and acknowledges the problem but the entire world of Chrysler seems stymied. One report on another site submitted by the owner of a '97 model described this same problem and a couple of similar problems appear on the NHTSA web site. The owner of the '97 model tried the process of elimination and replacing his driveshaft, wheels, rims, shocks and tires (in turn) to no avail. The strange thing is that this problem doesn't seem to cause any uneven tire wear even on the rear tires. Due to normal wear I've already replaced one set of tires and the shocks but the problem persists. The truck is not abused. I've had the rims and tires checked for balance at a performance shop and they're virtually perfect. The owner of that shop is installing a DNYO machine and is so intrugued by this problem he wants to strap the truck to it to christen the machine and see if he can duplicate the problem. In the whole world of auto excellence under the entire canopy of Heaven someone, somewhere must have some idea what might be causing this condition. There aren't too many things on a vehicle that go round 'n round that will make it go up 'n down........or cause it to happen. I'm open for suggestions.