when I hit 70 I feel like I'm swaying side to side a little. I have a 4 inch lift with 33 inch tires, but I have never had this problem through the 5 years I've had the lift. could it just be the allignment?
If it was the alignment it would happen at any speed.
I would be inclined to look at the tires and wheels.
Where speed is a factor often weight distribution can set up a harmonic resonance at a certain speed and cause a continuous vibration or rapid fluttering that might throw you off course. If it stops as you reduce speed then it is more certain.