In AZ we get temps over 120 degrees and we also have some serious hills. For those who aren't going to be using the truck for pulling a lot, save your money since a good gasoline engine will work. It just doesn't work as well. If you're going to be doing a lot of heavy towing, pay the difference because it will pay off in the long run. There is no wrong answer. Buy what you like. People were pulling most RVs with gasoline engines until a couple decades ago. They worked, even though they weren't as good as what is available today.