Check this out i have a brand new motor that now has 1200 miles on it. I broke it in using penzoil and had no problem with it at all. Yesterday I changed the oil and put Mobil 1 in along with a new fram oil filter. I have done nothing else. I took it out for a ride a couple time now and noticed that at cruising speed I have about 60psi of oil pressure but now when I get on it the oil prssure falls to about 40psi ( I have only done this twice to not risk any chance of hurting anything). Has this happened to anyone before. I have heard that the oil filter have check valves in them and we they are bad which happens sometime they don't allow oil to stay in the filter and keep the filter filled to full capacity. Any help from anbody would be great. Also the truck has a high volume oil pump in if that matters.