I was driving @ 50 mph when truck locked up.I had to put into 4Wlow to move off of road. Since this occured I have replaced rear differential but problem still remains!! I seem to get 4WhLow and 4WhHigh and 2WhHigh are still locked up. All is smooth in 4WhLow. How do I get other gears back to normal---is it transfer case? Need Help very badly with this !!!!! Thank You in advance!!!