What should I replace.

Hi, my name is Devin. I'm an auto repair expert with the Car Genius team at RepairPal. I'm so sorry to hear you’re having trouble with your vehicle. It sounds like your Aveo could be dealing with a few different issues. Since it started losing power on hills and during take-offs, then backfired and shut off, it could be related to the fuel, ignition, or timing systems. Backfiring occurs when unburned fuel ignites in the exhaust or intake system. Several factors can cause this: a rich fuel mixture, meaning too much fuel and not enough air; timing issues, where the spark plug fires at the wrong time; or issues with the ignition system, such as a faulty spark plug, coil pack, or distributor. While it's possible the new coil pack might be faulty, I do not believe it is the most likely culprit. I recommend having a professional run a diagnostic test to determine the exact cause and get your Aveo back on the road. 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!