First Drive after building, Major shake

I have a couple ideas I ran into with one of my darts. First, I know the tires are new but how much weight did they take? Could have thrown a small one when you got up to 50, you might not have noticed it, if it were right next to a big one or on the inside, also certain tires have heavy spots in them. I have had this problem with a brand that rhymes with SOOPER, if this is the case you will likely have a lot of weight in one certain area. I have seen tire techs grind the inside of the tire so it would take smaller weights likewise I have seen them grind heavy spots out of the wheels themselves, yes really, less likely to throw those weights then. Also consider the wheels. An old Mopar ralley could be bent, or warped a little bit, and I have seen wheel mounting machines bend wheels especially steel wheels. It would not take much of a bend or warp to cause exactly what you are saying, you can jack it up yourself and roll them and look for any side to side motion or a bad belt, remember COOP..... OOPS I meen SOOPER tires. You might want to unhook the e brakes, and change the other wheel cylinder. You said the drum brakes were new but did you turn the drums as well? I think I read you had new rotors on the front, were they trued up? A hot spot from certain pads could also cause this, again you can jack it up and roll it by hand and see if it scuffs or slowes down in a certain part of the revolution. Hope you find it, sounds like you got a nice ride. GOOD LUCK, JOHN.