I have a 2009 Duramax LML with approximately 185k miles that is all stock. I was driving on the interstate last weekend about three hours into a five hour drive. Cruise was set on 78 running about 2000 rpm. It was level ground with minimal boost involved. Out of nowhere, it felt like the truck lost power and had a noise similar to a belt or the transmission slipping. The truck slowed itself down and it felt like I was applying the brakes even though I wasn't. I pulled off the interstate onto the shoulder and before I came to a complete stop, the noise went away. Checked the belt, etc. and couldn't find anything. All gauges read normal and the transmission temp was around 180 which is normal cruise temp for the truck. Being in the middle of nowhere, I got back on the interstate and the truck was driving fine. About 30 miles later, it did the same exact thing. I once again pulled off the interstate to look and couldn't find anything. I drove another 100 miles or so to my destination without a problem. Two days later, about the same distance into the drive home, my truck did the same thing once, went away, and has driven fine since. I checked all fluids, etc. and everything looks good. Has anyone dealt with this before. I can't get it into the dealership until after the 4th of July weekend and am supposed to haul horses on an eight hour round trip. Thank you for any input.