All of this is overblown. Remember, anyone can sue anyone in the US for anything...and claim anything in their lawsuit. I can sue GM for my car turning into a rainbow elephant at night and haunting me in my sleep, and if I get enough people to agree with me, I can even make it a class action lawsuit. Doesn't mean it'll ever get anywhere. 9 out of 10 class action lawsuits end up vanishing.
Also remember that GM has sold somewhere in the realm of 2.8 million of these trucks, with probably at least half being 5.3 V8 w/DFM. Based on numbers on this forum and just extrapolating that, I'd wager that there's maybe 1000-3000 engines that have this issues? That's somewhere in the realm of 0.1% - 0.3% of total vehicles sold with this engine....
EVERY manufacturer has issues during manufacturing. Bad batch of parts from a supplier, issue with a line process, assembly error, etc.
If you have the issue, you just happened to get unlucky. Get the warranty service and go about your life.
It's hilarious when people say stuff like "Oh I'll never own a GM again or GM is so trash, blah blah blah blah" based on such tiny numbers. Have fun with Ford and Ram's plethora of their own issues.