tmacod

tmacod, Sorry it took me so long to get back to you. Yes I have used CAT DEO 15w-40 since my truck was new. I just switched to Amsoil synthetic 15w-40 to see if I could get better fuel milage and I've run the Amsoil for 10,000 miles now and I see no difference from the CAT oil. The CAT oil is blended by Mobil and is from the highest quality base stock. They add extra zinc and other additives to make it an extreme service and extended drain engine oil. I don't think you can find a better Petroleum oil. It is as expensive as a lot of the synthetic oils. I got it at employee cost. Let me know if you have any other questions. Regards, Mike.