So I just brought an 2012 Ram 1500 with the 5.7 hemi. I was reading the owners manual and its stating that I should change my oil ever 8,000 miles but the service pple told me to change it ever 3,500 miles.So should I change it ever 3,500 or 8,000 miles? and its all hwy miles and i drive about 50 miles day. Also I was curious about the type of oil it called for, 5w-20? should i stick with that or should i go with 5w-30?