i just changed oil in my 2002 5.9 i used Mag1 15w40 this time because its hard to get ahold of Valvoline Premium blue 15w40 like i used to use and we run Mag1 at work in the rigs...the factory oil pressure gauge seems to be reading lower than it did with the valvoline, any ideas? my manual says CF-4 is the oil for my truck but i read that CJ-4 exceeds CF-4 and the mag1 is CJ-4 i am changing to a different oil since the valvoline is hard to get ahold of in my area. what oil do you guys run in your trucks, and what does your oil pressure gauge read at idle and at normal driving rpm? thanks in advance