I know this is a post from a couple of years ago, but I had to respond in case anyone else is considering a similar issue.
Here's the beef on changing oil
viscosity in these engines.
First off, in 2011 GM changed the oil requirement so that the oil
used in these engines is REQUIRED to have the Dexos1 rating on them. At this time only synthetic and certain synthetic blend oils, and only in the 5W30 and in extremely cold temps, 0W30
weight oils are Dexos1 approved. The bottle HAS to say Dexos1 approved on the bottle or it does not meet this requirement. If there is any usable warranty on the engine, and it goes out, GM will not honor the manufacturers warranty if oil not having the Dexos1 rating is used.
At this time, Mobil 1
HM 5W30 does not have the Dexos1 rating in it, but, for instance, Valvoline Synthetic HM 5W30 does. I'm not sure exactly why Mobil does not have the Dexos1 rating on this oil, but maybe in the future they will add that. I have searched on the Mobil 1 website but did not find any reason why the HM 5W30 doesn't have the rating when the rest of the Mobil 1
5W30 and the 0W30 Synthetic oil's do. Even Mobil Super Synthetic 5W30 has the Dexos1 rating and it's in the conventional Mobil line. For that matter, Castrol's new synthetic blend oil
Magnatec 5W30 has the rating as well, and that's based on it's conventional GTX oil
So any oil used in any oil change in 2011 to 2013 engines must be 5W30 or 0W30
with Dexos1. 2014 and later 5.3L engines also must have the Dexos1 rating and MUST be 0W20 oil. GM did increase these engines to 8 quarts from 6 quarts oil
fill. Again, this is just for the 5.3L engine
and maybe 1 other like the 4.8L engine
. I believe the 6.0 or 6.2L engines are still 5W30.
Prior to 2011 back to 1999 when these series engines came into production, the recommended oil weight is 5W30 for year around use, but in any temp above 0 degrees, 10W30 may be used. The 2008 to 2010 engines highly recommend staying with 5W30 but 10W30 isn't prohibited.
Using High Mileage oil in these engines is owners choice and I only recommend using it when an oil usage or leaking issues are present. Otherwise, keep using what you are currently using as long as it is the proper weight and viscosity your engine requires. That's for any engine. Using High Mileage oil in those situations may not completely correct the issue, but should help slow down and MAY correct it. However, the situation may be bad enough that only an engine
rebuild may completely correct the burning or leaking issue.
Short story, your mileage may vary.