[Excaliber]

You do have the vacuum advance disconnected when your checking the advance I assume? It would be logical to assume the mech advance is indeed 20 at 3000, which would be added to whatever your base timing is.

Before you check base and add advance be sure your idle rpm is consistant, low enough to NOT impact the advance weights/springs.

When you call them to verify it's really 20 max also ask them at what rpm it BEGINS to ramp up.

Sounds like the advance mechanism is sticking or binding, not working smoothly.