Thanks again for the inputs. I thought the load may make a difference as well. I actually contacted a local dyno to see if I could run the same experiment under load. I was thinking large mirrors and lights to see underneath..... haven't had the time yet so I decided to start with a few reasonable parts.

The symptoms are vibration starting around 40 up until 65-70 then it reduces. The vibration is felt in the center of the car. I have replaced tires and wheels and rotated several times in the last year and no change. Two separate, fairly competent shops have briefly looked at it with no conclusion - that was my hysterical differential post a while back. The camera did record a squealing sound starting around the same speeds... may again point to the u-joint. The mechanic may not have dropped the shield and the sound transferred back toward the differential.

I decided to start with cheap/simple and see how things progress. The offset center bearing was an easy try, but in this case it didn't improve things. As I said, I am at 260K plus now so a center bearing may be worth a try. While the shaft is down I am most interested in the u-joint as recommended. I think my SDL is fortunate in not having to remove the exhaust ( single all the way back). I got the shield off before without removing the exhaust, so I'm optimistic.

Any idea on the turn-around time for the Atlanta driveshaft guys. I've done more Mooresville - Atlanta and back in the same day trips than I can count. If they can fix it in 4-6 hours I may just drive it down ( in another car).

Thanks for all the assistance and I will certainly post any results.

Chuck