I assume you also have the heat shield in place. I experienced this issue many times. Eventually went with high torgue starter, 00 cables and a heat sheild. It was the sheild that finally made this problem go away.
Nope, no heat shield. The key to coated headers is having it done both inside and out. Using an infrared thermometer you can check the exhaust runners right before they dump into the headers. Runners are about 400 degrees and the headers are around 250 degrees, big difference.
