My '46 that I just finished building likes to wander or dart as I'm driving it down the road. I'd say the problem starts at 35mph. My speedometer cable broke so I don't have the exact speed. It has 2.5" lift yj springs and is spring over. I put the rocky road high steer kit in too. New steering box as well. Have the ties towed in too. The tires are 34x10.5 TSLs. It has a steering stabilizer as well. Is it because I'm so tall that it wanders or am I overlooking something? I've driven a few stock trucks that do this as well.