very low oil pressure and even after the engine is up to temp when it is stabbed the valvetrain starts to chatter for a few seconds. i know this is a common chevy thing with the valve chatter but I have never had it while on the highway. And this last week when I changed the oil the truck went into a limp mode twice for low oil pressure (check gauges light), the gauge hit zero. My engine has never overheated nor does it knock. My 5.3 runs at 50lbs all day long 175,000k the blazer is almost the same way with 149000 but my suburban is very low 20lbs on the highway for the last few months. and now the valve chatter on the highway. it doesnt leak or burn any oil.