sometimes this is the beginning of a torque converter going bad. another indication would be if the vehicle shuts off pulling up to a red light or a stop sign, one way is to put it in neutral, as you coast up too the stop sign for example. I would try to put your truck in neutral before it stalls, so as you back up, instead of stopping then shifting, try to shift into neutral before you roll to a stop, and see if the vehicle stays running. Also if you type the words bad torque converter ? in the web search box, you can do a little digging and try to get some information. For some reason, it is common for lock up torque converters to go bad, not sure why, hopefully that's not your problem. best of luck