Today I went down to Cummins to pick up some oil and a filter to change on my truck. I was shocked when I discovered that Valvoline Premium Blue 15W-40 a semi-synthetic has been superseded by Valvoline Extreme Blue 5W-40 a full synthetic. The shocker was the change in price the Premium Blue ran about $8+ a gallon, the Extreme Blue doubled in price up to $17+ a gallon. Needless to say I just got the filter and am now wanting to switch to Chevron Delo 15W-40 which I can buy at Costco for cheap. What are the implications of making this switch form a semi-synthetic back to a petroleum based, if any? Thanks, Jason