Ignition problem???

Hi I’m 17 and building a 90 d150 with a 318 magnum carb swaped. I’m having an issue with my ignition box I believe. Truck starts and runs for a little bit runs great then missfires and dies (can start right back up and runs fine then repeats). I was having a high rpm breakup also but I bypassed the ballast resistor and it seemed to help. Idk if it matters but I’m running an orange box and a blaster 2 coil. only getting 3.5v at the coil when testing with coil ground and 13v if I check with a body ground. I thought it was the carb but I’ve tryed my buddy’s known good carb and it still did the same thing