Tsaint10

About a week ago I put my truck in reverse and an awful grinding sound came from under the truck. The next day I noticed my truck wouldn’t go into 4wd low. The day after that I was driving down the road in 1st or second gear and my truck wouldn’t shift. Now it is stuck in 4wd low and will not come out. I’ve replaced the transfer case motor, the 4x4 actuator, and the transfer case control module and nothing has worked. I was just wondering if you had an idea of what it could be ?