If its black, its dirty and needs changed. Every 3500 for me.
I change the oil in my 2014 Yukon (130,000 miles) whenever the computer says it needs it, usually around 7500 miles. 100% synthetic and new filter.
Amsoil = best oil company out there. Lubrication is their specialty.
They recently changed the formula for their SS. Viscosity are not what they were. Probably trying to meet the upcoming GF-6 cert. Additive package still looks good, but the lower viscosity at operating temp has been causing some issues with people.
Otherwise, yes, Amsoil is an excellent oil. I, personally, still don't put it above Redline. At least in wear protection and shear strength.
I appreciate all the advice and opinions, but I really didn't get much further, lol.
I think I'll start with an oil analysis and see what the lab says.
I prefer dangerous liberty over peaceful slavery.