While traveling on a local highway in the far left lane, the engine completely died (no engine light came on). I was trying to negotiate traffic while getting to the shoulder of the road, and the transmission began shifting itself into park. I grabbed the shift lever trying to prevent it from going into park; however, it did just as I reached the shoulder of the road. At this point, I had slowed to ~25 MPH, but it still locked the tires up and slid a few feet. After turning the key off, removing it from the truck, and opening the door, I was finally able to restart it and I went straight to my local mechanic. He attached a code reader; however, there were no codes displayed. He stated they probably cleared out when I restarted the truck. This happened a couple of months ago, but my wife has been fussing at me to report it.