I added a second ground wire from the battery to where my alternator bracket attaches to the block on the advice of Coolerman. That, with the starter ground strap to the frame, ensures the battery, alternator, and starter are solidly grounded. Eliminates grounding gremlins.
Have you put...
You could also check to make sure your negative cable has a good ground connection. Might as well check the one from the starter to the frame (if you have one on the 3B) while you are at it.