Baker,
I think nobody mentioned this but be sure to check that the damper hasnt slipped either.
That is, is Top Dead Center where it should be?
You can really only check with the head off, but if it slipped a LOT you can tell thru the plug hole.
Put a dowel rod into the #1 plug hole, then rotate the crank til the DOWEL says its at TDC best you can measure it. Then see what the damper marks say. Wont be exact but they should be close.
I figured, to run as slow as youre running, either
* Speedo is way off, like doing 90 but it reads 60
* Brakes are on or a bearing almost frozen
* Really bad tune
* Cam gear is a couple teeth off
* Crank damper has slipped 20 or 30 degrees ie a lot
Gotta be something big and obvious (once you find it that is)
Good luck
