Exhaust valve tip failure.

[Jedibusiness]

I’m out, too old to keep track of what bow tie tribe goes where. 

[L86 All Terrain]

You did pretty well, most work trucks in Canada are resting in the junkyard with that kind of mileage. 6L's fail within 2,500 miles, or at 200,000+. You don't see many fail in between there. Looks like you caught it before it really messed up your day. Good luck on your rebuild, and a happy 193,000m more. 

[Jedibusiness]

I think your spot on.  The 300K+ mile club is for non work related driving.  My mechanic, who knows how I use it, was shocked I got that many miles out of it.  Key is I drive rpm instead of speed limit.  Do my best staying just below 2000 rpms and only go higher pulling over mountains.  Where the 6.0 and 4:10 really shines is slow rolling hills.  Transmission drops a gear and up shifts at the perfect moment.

 

I've demonstrated how to tear a small block apart, now the measure is can I get it back together and run without issues.