Check your grounds, and Check your voltage to the distributor too, maybe check it at first and then after it starts running bad. maybe your losing voltage?
I love the mopars but I also have a 302 in my toyota. Its my "daily driver" :burnout:
He had the carb changed before I could get over there and it was running rough but it felt a lot different. He got it back to the shop and looked everything over and realized he forgot to hook up one of the plug wires. Took it out again and it ran like a top. New Holley dp is on it's way!