My father in laws 2001 gmc 1 ton crew dually with 8.1L randomly quits. There is no check engine light on, it doesn't sputter or anything like that it just seems like someone shuts it off. It will start back up after few seconds if not right away and then it could be fine for days before it randomly shuts down again. The truck has just under 160,000kms and is serviced regularly. It runs the same as when new has tons of power and is actually decent on fuel. Any suggestions?

 

My truck was doing that and it was the double positive going to the battery. It has a long bolt and there is a lead spacer between the 2 terminals. The lead shrinks from years of tightening and will cause a bad connection. I am not sure if the newer trucks have this same set-up (mine is a 98), but it was as simple as putting a small washer in there to take up the slack. You can also buy a new bolt and spacer from the auto parts store, but I had the perfect size washer in my collection and it has been working for months without a problem that way.
Besides that it could be an ignition switch issue. Good luck!