I've got a recently rebuilt motor that runs great off idle but shakes at idle. The vacuum is only 14.5-15 inches. That seems low to me based on my experience with V8s. Is this normal vacuum for this motor. Could it reflect a vacuum leak? Any other ideas.

 

Not a very good answer, but in a 1.8L corolla efi engine, the map sensor reads ~14.6 (don't remember if this was engine off, or engine idling, it's just a number that stuck in my head) but there is no reference to what the measurement actually is, possible it's the same. V8's I could see having more vacuum based on the fact more cyls, and likely much more displacement, but I don't have first hand experience.

 

Here is a capture for you, not a great angle or a calibrated high resolution meter..
that is around 15 at 750 revs idling.

 

Something isn't right...

I live in the same general area and altitude as yourself and pull a rock steady 21" at idle with 200K miles.

Check for vacuum leaks, proper firing order, and ignition timing. Sometimes things can get bit tricky like a stuck EGR pintle, leak from the internal brake booster diaphragm, improper fuel pressure readings.

Keep at it.