I have to say that disconnecting the alternator has a good chance of eliminating it, but I'm not sure that it will still give the answer your looking for. I tried to look at all the suggestions and the only thing I could come up with at this time was grounds. There are a lot of grounds and for good reason. "What doesn't go out can't go in". Starting with the battery. Check both ends tight and connected. If/when you get started go start moving each ground and I don't just mean a little. Move like you mean it and if that engine drops off you may have found it. Try the fuel pump, try the battery, ECU connections, Hell...Go change the air in the tires. The problem is their...it's just figuring out what it isn't. You'll find it soon and I'm sure. These are good lessons for when off-roading in the middle of nowhere.