I'm not familiar with the pertronix setup, but if it has it, can you check the gap between the reluctor wheel and pickup? That's the first thing I think of when people have this problem. My dad's car had that problem and we found the reluctor gap (on a MP distributor that came with the electronic ignition conversion kit back in the day) was too wide, so the heat widened it and no start when hot. We tightened it to .007ish and that resolved it.