[Don]

Had the same problem. If the no cost or low cost fixes do not work, I installed the following and the problem went away:

MSD 8584 Distributor, $190 from Summit
SUM 82005 Hi-torque starter, $160 from summit

Since both were installed at the same time, not sure what contributed to the fix. The stock starter was bench checked as OK. MSD Distributor allows a great deal of flexibility in the timing and advance, check their web site.