ifor a chevrolet truck to get past 300,000 some one isnt telling the truth someware...that enige had to be replaced right?


??
Could REALLY depend on how the guy drives it too. If he is one of those guys that simply never gets over 2500rpm then the total number of revolutions the motor did in its life is going to be much differnt than someone that runs an engine up to 5,000rpm all the time.
So the miles driven is one thing, but the total time the motor was running vs. the miles driven vs. the rpm will make a big difference.
This is why an OTR truck can go 1,000,000 miles for the same work a city truck might need in 20,000 miles.
One other thing to consider is that this truck seems to be moving ALL the time. So the oil is staying up in the parts. A truck that you rarely drive lets the oil settle in the pan and then the first minute of start up there is no oil on anything. Heat cycling of parts.......Lots of reasons a truck being used will last longer than one that only makes short infrequent trips.