My son bought a 2013 1500 5.3 14 months ago that now has almost 40,000 km on it (24,000 mi). Someone wondered how 15W40 would work in a 5.3 so I tried it for 10,200KM from 23,100-33,300.
The uoa indicated 2.5% fuel, a copper spike, (which indicates he is into the oil cooler)
lead at zero, which was my biggest concern.
The ZDDP was down far enough that extending the interval is not in the plan just yet.
The fuel dilution, possibly from the cylinder dropping tech caused the 100C to drop from 15.1 to 13.5.
There is still breaking-in going on, but other wear metals are at near zero.
I replaced the 15W40 with the same brand of 5W40, 6,000 miles shows 22% oil life remaining with 95% highway and 10 weeks use.
Next week my daughter is trading her 2013 Matrix for a 2014 5.3 GMC, the same as her brother's.
(Her father in law was an engineer at GM (retired) and I have a friend who's family has 18 GM dealerships, so the grandson bleeds Chevy orange.)
Will or do I use 5W20?
No, but I don't care or worry about warranty.
I've never had to.
I'll use 10W30 CJ-4/SN of any brand.
I always change the original oil asap and it never looks like anything you would want to put back into the engine.
Some manufactures like Mercedes Benz do that before the vehicles leave the factory " We go great lengths......so you don't have to" it says in the owner's manual.