I know everyone has their own, usally STRONG opinions on engine oil. My question is pretty simple. I like and have used mobil 1 for years. I read on the bottle that I can use mobil 1 truck and SUV oil in my Duramax. The only thing is it is 5W-40 when the manual says that the preferred weight is 15W-40. I noticed that the Rotella Synthetic is also 5W-40. Is either of these oils OK to run even though they are 5W instead of 15W. I will be towing a camper in the summer. Thanks