1972 C10 Steering Problems

[WhiteC10]

I have a 72 C10 Cheyenne Super. We just got the suspension fixed, the previous owner had lowered it without a notch kit so the frame rails would hit the axle everytime you went over a bump. Now that is fixed driving down the road it has a hard time going straight, anything over 30 MPH is almost impossible to control. It goes from side to side and is all over the place. Does anyone know what the problem could be? It does have power steering.