Cadillac Repair: cadillac vibration, wal marts, force test

Question
I own a 1993 Cadillac de Ville and it has given me good service through the year.  Of course, I am very tuned into it and repair whatever it needs.

Lately, I bought some new tires and noticed a vibration; I felt everything in the road.  I replaced the tires with new Coopers (which I have bought for years--the others were Wal-Marts Goodyear Viva touring tires.  The Coopers are a little quieter but I still feel the road and vibration.

I have had a tune-up, a road force test, checked the struts, the cvc joints, the wheels, etc. etc.  Now I'm wondering if maybe I need new engine mounts.  I'm going on a long trip soon to AZ and need to find out what is causing the vibration.  Help.

Answer
If you had NO VIBRATION with the original tires and now with new tires you have a vibration is it either due to a faulty tire or improper tire balance. Do you have a CHECK ENGINE light illumination on the dash or any other light displays or messages in the message center ?.