Please help Steering problem

I was in 4 wheel drive on the beach on Chappaquiddick. I went down a long trail that had no place to turn around. To get out I gunned it in reverse and spun the wheel to do a 180. Since then my steering is no good. It feels like I have no power steering when going slow. The steering wheel is tight, and it doesn't return after making a turn. (Normally when I finish a turn I just let go and the wheel comes back to the direction the truck is pointed.) Sometimes it goes back to normal, but when I go fast like on highway it starts again. Properly functioning steering is When going high speed power steering is less sensitive, when going slow power steering kicks in to help make those tight turns. It's like my truck gets stuck in high speed mode. It seems to be worse right now because of the bitterly cold weather we're having. Tell me what is wrong?