I remember a time driving out of jackson hole and into abig blizzard. iwas drivinga suburban 2500 an older one maybe 89 or so It was snowing very heavily. Iwas in 4 wheel drive the whole way . You couldn't see far enough to go over 35 or 40. snow was 6 inches deep unplowed and I was cutting tracks . wipers could keep up withthe snow and would fill up with snow evey mile so had to stop at every underpassand wipe the snow off. There is no way youcould drive 70 in those conditions. I am pretty sure that suburban had a regular 4 wheel drive unit that you had to shift into 4 hi to be in 4wheel drive. That truck was a beast !