I have a question for you oil guys. On my first oil change I used valvoline full synthetic and the cheapy oil filter that valvoline puts on the vehicles. When ever I get on it the oil pressure would go up like normal at the higher rpm's. On my second oil change I switched to castrol high mileage and the fram high mileage filter cause I have 91000 miles on my 04 titan. The first night I drove it the pressure would rise up like the valvoline and then some but now the oil pressure doesn't hardly rise at all past normal unless higher rpm's close to 5000 rpms. Is this the difference in the oils viscosity why it reacts differently? Thanks for any help you can give me.