There was light snow so I used 4 W drive on back roads to get to highway Rte 101 in Epping which was in good condition except for continuing snow. I switched to 2 W drive and immediately lost all steering and control of truck. Felt like wheels seized up. Went off highway and down 50' embankment hitting small trees and brush with driver's side for a reasonable crash landing. Truck undrivable was towed away and I am working with adjuster and mechanic.