vibration at 25-40 mph

OK. I called a local driveshaft guy. In the course of our conversation he pointed out that there shouldn't be any sideways play in the rear u-joint cups because of the c-clips being held in place by the straps. Turns out I had failed to install the c-clips on the cups that mount to the pinion yoke. Yeesh. No wonder I had problems! This afternoon I'll take the driveshaft for balancing.

Also, after I removed the driveshaft to install the c-clips, I remeasured the angles. New measurements:
trans seal 2 degrees down to the rear
pinion yoke 3 degrees down to the rear