Garak, Both of those engines showed sever camshaft lobe wear on the lobes towards the back of the engine. The front lobes checked out fine. There was no sign of sludge build up and the oil and filters were changed on a regular basis. The oil pumps were also working correctly. Never could figure out why the wear was so bad in the same area on both engines. I replaced the camshafts and timing gear / timing chains on both engines along with new lifters (all AcDelco replacement items). After that, I got 100,000+ miles out of both vehicles with no further issues. Do you have any incite as to why the wear would have been localized to the rear lobes on both engines? Both vehicles were purchased new and no internal work was ever done to the engines prior to tear down to replace the camshafts.