Im pretty sure it is your wheel(s) out of balance, maybe its also out of alignment. When i first got the car, shook bad, new tires, alignment helped, warped rotors replaced, then wheels balanced, problem solved, i pratically drove a 2-hour roadtrip with no hands half the time
(ok maybe not seriously but thats how smooth it was)
Wheels unbalanced get increasinly unstable as you go faster, mine was shaking at 65+
Sent from my DC4