Boy’s 03 Denali 6.0 lost oil pressure at 235,000 miles. We tried the overfill the crankcase trick and that didn’t work. We found another engine with about 135,000. We resealed it buying all the special little tools and swapped it out. Runs like a top. We’re going to tear the other one down and see what’s what. Maybe cam bearings. It’s in great shape and his wife loves it.