HELP!! with my 75 Dart

I can see that one now. To me, it does sound like you have a vacuum leak somewhere as noted above. The first part of the vid, I can't tell if it's wind noise, or uneven popping noises out of the exhaust.
Have you checked the plug wires to see if the order is correct?
Again, there are people that are FAR more knowledgeable on here than I am.