I have a 2001 4x4 Silverado 1500 I bought it with 35 K miles and now she has close to 275K I have changed the oil myself but mostly I use the local quick drive in and out oil change place. They keep asking me if I want to use the high mileage brand I have used the GM recommended I cant remember right now but its on the oil fill cap. I have used Pennzoil, Castrol and Mobile and have changed the oil every 3000 to 3700 miles I also have the tranny serviced every 50K miles truck runs great and have never had any drivetrain or internal motor problems I have been waiting for the Vortex to give so I can swap a new crate motor but she just keeps trucking

 

Own a 1999 Silverado 5.3L was with 82K miles. I've used multiple brands of Synthetic (Castrol, Valvoline and Mobil 1). I can say with confidence and experience that my truck runs quieter and smoother on Mobil 1 Extended Performance 5W30, along with a Napa Gold (Wix made) filter. This is the combo I intend to use for the remainder of its life due to testing other brands of oil/filters.

 

Not a bad combo, for sure.