I have used Valvoline durablend in my '99 Ranger with 3.0 with about 165,000 miles for the last 50,000 miles or so. Prior to that Valvoline dino. In my wife's 2005 Yukon ran Valvoline Dino till about 8000 miles and switched to durablend. It now has about 12,000 miles. I am considering switching to havoline since it seems to be a favorite here on these forumns. Would there be any harm in switching from the durablend back to havoline dino and would I be likely to see any decrease in gas mileage or engine life as a result ??? I do 3000 mile oil changes.