Is my coil to blame???

I have a 360 in a 68 dart. electronic ignition conversion. beefed up to 425hp at crank. I went to the chrome ignition box per this site and also put in a pertronix flame thrower coil. Ran Fine. Put new demon crb 750 ran fine. Very fast. for months and months.Then wanted to go old school and put a mallory 29216 coil on and it lasted 10 min. and gone. Didnt run. Got a replacement and ran fine. Yesterday in traffic not hot but not moving it started to die all the time. Would start no problem-Rev-no problem. in gear it died. over and over. would not run in gear.Got it to curb waited 20 min runs like a champ now. WTH? Is the coil lame or box going out? Sorry for the long info but I dont want it to happen again. What coil do you guys run with the chrome box.
Thanks Dale