This morning I was behind a โ€˜12 F-350 Super Duty with the 6.7 Powerstroke, identical to the one pictured. It was super icy out, and at one point we got to a hill and the truck lost traction and stopped moving forward despite being in 4WD. He slid around sideways for a moment, then stopped for a second after bouncing off the curb, then proceeded up as though nothing had happened. Does the F-350 have a locking differential? And is locking the differential likely what he did?