what makes it diesle sometimes

Hi, my name is Devin. I am an auto repair expert with the Car Genius team here at RepairPal. I'm sorry to hear you're having trouble with your vehicle. Intermittent issues like the one you're experiencing with your Sierra 1500 can be tricky. If the engine is "dieseling" or continuing to run after you have shut the truck down, it could be caused by various things, such as improper engine timing or other internal engine concerns. The fact that the problem is intermittent makes it harder to pinpoint, but getting the vehicle scanned for trouble codes might help identify if any specific sensors or components are malfunctioning. If you need more advice, have any other questions about your vehicle, or would like to get connected to a RepairPal Certified shop near you, we have you covered. Give us a call at 877-913-1554, and we will happily help you out!