Now seems to be over. Got her all together yesterday, and all seems well. The weird vibe is gone, and so is a weird noise that I had been ignoring. I imagine it was actually those spline cup teeth wearing away.
I still think my old driveshaft was fine. In a side by side to the new one... I saw no difference other than color. But for $70 it's got ALL new parts now.
Woo Hoo. Gonna try to ride her 50 ot 100 miles later today for a proper shakedown.
Thanks everyone that helped talk me thru this.
This club sux!

Jabba