I appreciate the help guys. I wanted to stick a fork in this post by providing the solution to my problem. In the end, the substantial vibration was caused by a collapsed motor mount. Lee, and others, provided the answer, but I had the blinders on and I refused to believe it. I had just replaced both motor mounts less then two years and 20,000 miles ago. I couldn’t believe that they had already failed. Well, the mount on the passenger side had collapsed to flat. Those were aftermarket mounts I purchased through Performance Products. They were out of warranty of course. I went to the dealer for the new set. Hopefully they will hold up better.
I can’t believe the mount failed in such a short time. At least it was a learning experience for me.