I have considered the transmission as the source but will approach that as a last resort as anything transmission related work is expensive. The vibration is intermittent. When the car first starts cold, there is very little vibration and some days there is none. After a few minutes, the vibration increases and after driving for more than 30 minutes the vibration is strong. Pulling up to a red light is tough as the vibration reaches its maximum just as the car stops.
I read in many places that vibration on a 4 cylinder engine is normal and that all 4's will vibrate. I disagree. I have owned 4 cylinder cars for the past 40 years and the Focus is the first that has given me vibration problems. All the others have developed a shake if there was a vacuum leak or a bad plug, but I have never had a vibration like this.
I'm thinking I may have the fluid changed and the transmission adjusted after Christmas as I know it will be over $250.00