I would have that 4x4 switch checked. I know of a 93 right now that is sitting due to the 4lo kicked in at 70 mph and cooked the trany. That might be the jerking, so best to either get it checked out or make sure you are in 2hi and unplug the switch and see if that makes a difference.
Don't want to see you post, "Replacing Trany due to 4x4 switch"