I have the exact same thing.
I tried to bring it into the dealer, but they say they cannot drive the car over 70mph to check this.....so no fix for me.
Therefore, mine still vibrates.
keep taking it in for the vibe, then after a few attempts, ask someone at the dealer (pref. the sales manager) about a lemon law buyback and who you should speak to. I tried this, and in two days (after six months of trying) they had a Ford driveline engineer down to examine the car. I demoed it for him, and they ordered a halfshaft, driveshaft, some assorted other components, and a balancing kit. Got the car back three days later w/ no vibe!
It was really bad, too. Above 80, and the mirror would shake. Above 100, and the whole rear end was buzzing away.
Cant beleive this crap is still going on. I had one of the first round 03's and went thru 3 drive shafts before they got it right. Got the same BS about cant drive over 70. Finally asked to speak with the service manager and took him for a ride. No other advice for you other than to not leave until they provide some service. Have them call SVT, this is a well documented issue.
I brought my 03 about 3 months ago for the vibe. My driveshaft was ok, however, they did replace the rear end assembly. Keep this in mind if it continues to happen.