454ss

when this happens the front end isn't engaged, just the transfer case, I had it scanned today and there are no codes.

I don't see how any thing in the case could cause it to do this, when it goes to 4 low the range selector is being moved by the shift motor.

2002 2500hd with np1 transfer case rpo. it started grinding while driving and the service 4wd came on so I stopped and when I went to go again all the lights on the 4x4 switch were out and the transfer case was in 4 low but the front end was not engaged and it would not come out of 4 low. I took the switch out and tried it in another truck and the lights came on and it worked like it should, so the switch is ok. the 4x4 fuse was good, the atc fuse was blown so I replaced it and the lights came on the switch but it popped as soon as I tried to take it out of 4 low. so I took out the transfer case control module and it had a burnt smell to it so I replaced it, no change. next I replaced the shift motor on the transfer case and everything worked again so I thought it was finally fixed, but I took it for a drive and after about 10 miles it went in to 4 low again just like before. im out of ideas, any help would be greatly appreciated!