I was driving at approximately 25-30 MPH, accelerating from a stop light and I felt a clunk, heard a grinding noise and my back wheels locked up. It was snowy/icy conditions so the back end of my pick-up slid out to the right a little bit before the wheels unlocked and I was able to regain control. I could have slid off the road or into another vehicle had the wheels remained locked. The computer system then alerted me to a transmission issue and to reduce speed immediately and call for service. The pickup was then unable to shift out of 1st gear. The vehicle has been towed to a dealer and I have been informed the valve body in the transmission has to be replaced which is 8-12 weeks backorder.