My nephew bought a 2007 Chevy extended cab w/either the 4.8 or 5.3 (I haven't looked yet). It has 175k miles on it and has low oil pressure. He has replaced the oil pump and the oil pressure sending unit and it did not fix the pressure. Also when he changed the oil it was pretty thick w/some sludge. My guess is that the sludge has clogged the oil guides (or whatever they are called.) What say you gearheads?