Originally Posted By: nomochevys
... The last oil change was an eye opener for me. The filter was full of sludge and when I pulled the drain plug the oil came out in clumps to some degree...
I had exactly this sort of thing going on with a 1999 Suburban 5.7L Vortec a few years ago. It turned out to be antifreeze leaking into the oil because of a bad intake manifold gasket. A valve lifter had started making noise before I found the oil to be a mess. A quart of Marvel Mystery Oil mixed with 4 quarts of Shell Rotella 30 weight [a diesel rated oil with high levels of detergent and dispersant that make it excellent for cleaning] quieted the lifter in the first few days. Then I replaced it with the same mixture after a week and ran it another 1000 miles or so for general cleaning. I used Rotella synthetic 5w40 after than and put something like another 50,000 miles on that truck, if I remember correctly, before trading it two or three years ago. As far as I know, that engine is still running for the new owner.
I don't know this particular engine very well, but I'd definitely look into the antifreeze-in-oil issue if it were mine.