I need the expert opinion of all my fellow oil junkies here on BITOG. Application is a 2003 Chevy 2500HD 4x4, 8.1 Allison. I bought it a few weeks ago with 27k miles on it. I immediately did a full fluid and filter service. In 1600 miles so far it has used about 1/3 qt which is great for this motor. My one bad vice in life is that I can't stop my addiction to home brewing my own oil combinations. I know what many of you think about it but when I try to stop I can't. Is there a 12 step program in my future? Anyways, 90% of my summer driving is at speeds of 70-80+ mph, cruise and AC on high, interstate hwy, open road driving. On the way out I hit a low temp of 45 at night in the Rockies and a high of 115 just outside of Death Valley. While making sales calls in So Cal it has been lots of 85+ degrees bumper to bumper traffic with the AC on high. But like I said, it is a 90% open road with 10% heavy city traffic conditions. My oil mix this time is 4 qts Mobil 1 10-30, 1 1/2 qts Chevron dino 10-30, and 1 qt Chevron dino 30w. Delco PF454 filter. With all the info above, what would you suggest for an OCI? Thanks to all of you for making my addiction worse! Vern.