Two questions: First, I use Havoline conventional 5W/20 motor oil in my 2005 Dodge Grand Caravan. I generally change oil every 3000 miles. Lately, I have gone 4000 miles. Any harm to going 4000 or should I go ahead and change at 3000? Secondly, the Havoline is GF-4, which I understand to be about the same as API SM rating. The DaimlerChrysler requirement is MS-6395(?). What API rating is this equivalent to?