Purchased my 2012 Ram Big Horn in Jan. In May with only 3530 miles, the change oil light came on. I figured the truck was at the dealership for 2 months so it was 6 months old. The book say to change the oil at 8000 miles or 6 months. I changed the oil with Mobil 1 5w20 syntetic. Now 3 months later and 7500 miles on the truck, the change oil light is on again. The oil looks clean and full. Any suggestions?