damper

If your engine runs rough only under a load at high rpm then itis more likely to be an injector or so some other fuel related issue.

The vibrations caused by a bad dampner are usually most noticeable at idle or under light load at cruising speed.

 

With the engine Idling take a length of heater hose and put it close to the dampener and the other end listen if it rattles it is junk, if it wobbles it is junk. The true test is to remove it and on the tire bounce it about 3 inches if it rattles it is junk.
For a rough running engine, test the CAC, a cylinder cut out test, a top end set, fuel filter change, fuel pressure test, and inspection of the return fuel for air. That should cover it.