While driving down the interstate truck suddenly down shifted causing everyone in the vehicle to fly forward. I shifted truck to neutral and pulled to the side of the road. When I started the truck back up transmission would not shift out of 3rd gear and then went down to 1 st gear the truck and back to 3rd never getting out of 3rd and the wrench light came on. Took to the mechanic they said the lead frame was bad but the the computer had also thrown a fatal transmission code, and that I would need a new transmission at a price of $8000. I have tried to contact and look up a recall I can find them on other trucks but says there’s not one for mine