Hi all. First time I’ve ever posted on one of these forums and I’m only doing this because I’m not sure where else to go for help. Over the winter I built a 400horse n/a 306. Msd 6al box is the only electrical add on to the ignition I’ve done other than a tune (chip). I drove the car in the colder weather and had no issues but now it’s starting to heat up I can only drive the car for about 30-40 min before I heat soak something in the engine bay causing a misfire that starts small then becomes very bad after a while. When I pull up to a stop light the car will surge at idle then fall on its face. It will always refire and I pedal it to keep it going. I let it sit for a few hours come back fire it up and it’s as though nothing ever happened. Runs great! I’ve swapped out the icm. Put in the old distributor (oem) did have an msd distibutor. Put the old coil back in and changed all my coolant temp sensors. I’m lost. Have no clue what it could be. Car runs about 180* on the coolant side but when it hits 190 is normally when this starts. Any help is greatly appreciated! Sorry for such a long write up!