In my search for vibration causes, I seem to have made more. I bought all new half shafts and had their balance checked at a driveshaft shop. All good. Drove 6K and vibrations slowly increased during the trip as well as a curious high frequency growling/rattle sort of sound. Got home and the new inner yokes were loose on the output shafts (I have a twin link system). Swapped in the old inner yokes and all is back to normal again. Yet another thing to watch for!