Hi i recently noticed the oil gauge going low from 20 to 30'is Psi on start at idle then running goes up from 40 to 60 Psi , i would think it should be at 40 Psi from the start like in my Sierra stays at 40 from start and only goes up from there but the van stays in 20 to 30 Psi at idle even when the engine warms up i wonder is this is normal on this vans ?

 

I have 325k miles on my 6.0. What you described was happening to me recently as well. My mechanic said a failing oil pump is what wrecks these motors. He put on a new high-volume (not high-pressure) pump and it's back up to where it used to be.