So I am currently using Valvoline Conventional 5w-20 oil in my 96 4.6L Thunderbird's engine. Ford, the owner's manual, and different owners I have spoken to all say use either 5w-20 or 5w-30 weight oil. I decided to use the 20 weight to maybe free up some horsepower but now my oil pressure is low. Not dangerously low as to cause problems, but just below the "n" on "norm" on the reading in the gauge cluster. Is this from the oil or from another issue? Thank you.