I had this problem for a long time in my 2001 jimmy. It would shift in & out of 4wd hi on it own all the time. I replaced the selector switch, the TCCM and it did not go away. It turns out the vacum switch on my transfer case was bad an let fluid into the vacum lines. Crawl under your truck unplug the vacumn line from the top of the transfer case and see if any fluid drips out. If it does you need to let the lines drain and replace the vacum switch. It worked for me & I have had zero problems since. It is a lot cheaper to replace the vacum switch
