Got a Ford 5.4 f250 super duty from 1999 4x4

I bought et a year ago. And just after I bought et I had it in 4low and the transfer case made a grinding noise and the truck would not move. I put it in 4high and the problem was gone..

I thought the 4 low just was broken so I just stopped using it. Then a couple months ago I drove in 4high again down a mountain road and the truck made the same noise again and I loose power to my wheels again. I stop and try to put it in park but it just sounds like a machine gun from and the truck still roles. I play with the stick From 2wheel to 4x4 and it makes a clunk noise and the truck can move again. But not for long now it pops and in 2wheel drive. And I get the truck towed...

 

Well, it sounds like first, something went wrong with 4Lo, and that resulted in some chunks of loose metal in the transfer case, and then when you used 4Hi, some of those chunks did their work on the rest of the case. The transfer case likely needs to be rebuilt.