To much build up pressure in coolant system!

Hey guys, I was driving to Carlisle from New York in my 72 slant 6 Dart. Went 100 miles and stopped for gas, but I got out and saw white smoke and coolant puking everywhere. Coolant overflow tank had a hole at the bottom. Checking that the radiator was not leaking (its not), I figured maybe the overflow needed to be replaced. Limped out to Napa and got coolant, overflow tank, and new radiator cap (vent was getting sticky and cap was hissing). Drove maybe 10 miles and checked it. No overflow anymore but a lot of hot hot hair pressure in the overflow. Thought it was doing okay so was driving towards home. Didn't go more than 20 miles before white smoke filled the cabin and under the hood and I heard a horrible noise. Pulled over and shut off the car immediately, while the noise continued. The overflow host blew off the radiator and sprayed hot coolant everywhere! Ended up getting my car towed to the end of a disappointing day. In questioning my 180 thermostat, by both it and my water pump are new as of last year. Pulled my oil dipstick but no milky oil. Help would be greatly appreciated!


EDIT: want to add that the idle got pretty rough a couple days before this, like a misfire during idle and under acceleration then a stumble under hard acceleration. When driving on the highway, I had a sudden loss of power for about 5 seconds where it was stumbling horribly and the throttle did not help. I finally mashed the pedal and it gained power. This happened before the coolant problem. I have good fuel delivery looking down the throat of the carb. The misfire is intermittent.