When under a load from 3000-4000RPM my Jeep vibrates noticably. I've got just over 20,000 miles on it and never felt it before. I did remove the dampener built on to the rear T/C output when I changed the driveshaft but would expect that to only relate to wheel/drive speed not engine RPM. Am I alone here?

 

Vibrations are hard to troubleshoot. I would ask questions like is it always there at that RPM or is it intermitant? When did it start, and what was the last thing you did before it started? How long after you did something did it start?
its the vehicle stock, or did you install a CIA and new conical filter? Does it feel mechanical, or something else, such as the engine starving for fuel or air?
Why did you change your DS and why did you not re-install the damper?
Sorry I'm not more help but you've not given alot of info.
The first step to troubleshooting a problem is to ask what has changed just prior to the problem.