My '37 still has the straight axle, and normal highway speeds for me are 65 to 70 mph. I do keep a close eye on whats going on around me, a sudden move is not going to be like a modern truck! I doubt IFS would change that fact, these trucks are just to high centered for real evasive maneuvers.
Mine does ride like a truck, a nice truck, but still a truck.
Joe
