Rolling Feeling

There is all kinds of different things that could cause vibrations. The best advice I can suggest is process of elimination. I would make sure it isnt the engine causing the vibration by eliminating the drive train. Simply put it in Park or Neutral and rev the motor until it gets to the RPM that the vibration occurs while going down the road. Then you can check the drive train by setting the rear of the car on jack stands, crank the engine, foot on the brake, and put in in gear, let your foot off the brake slowly. I had a ticking noise under my truck and just couldnt find it going down the road. I did the above and crawled under the truck with the drive train in gear. I went right to the noise which was in the rear end. The carrier had failed and I had to replace it. Now the above described will not do any kind of diagnostics to the front end, or wheels.

Another way is get up to speed until you feel the vibration and shut the engine off. You might get a better idea what is causing the vibration.