excessive shaking(tire balancing?)

i drive a '99 f-150 with 70,300 miles on it. this problem is comes and goes. when i'm driving down the road doing atleast 45mph my truck will start to shake and it gets worse until it feels like the wheel is falling off, if i come to a complete stop then go again it is o.k. it does not happen all the time, and might happen after driving at higher speeds for a few miles. i had this problem before and went and had the tires balaced, this seemed to do it again. it has been fine for the last 10,000 miles. I just rotated my tires and it is doing it again, could i need them balanced again? or is this another problem?

Try checking the tires, maybe there is a busted radial?

check lug nuts, may be lose.