i have a 2004 2500hd 4x4 with 154k on the truck now and it runs like a champ. i started my truck after being home for about 30 min. to go to town and the oil psi was at about 10 pis and i could here the lifters taping. the truck ran fine on the way home from work. i shut it down and have not driven it. i did change the oil filter and it didn't do anything different. so i'm thinking it is the oil pump or the pick up tube o-ring. i would like to test the oil psi at the filter, but i don't know if there is o test port. any thoughts?