6 to 7 thousand miles on full synthetic. '14 Silverado 5.3L. Do notice some loss of fuel mileage after about 6K, perks up again with an oil change.
Did my own oil changes until maybe 8 years ago. Havoline 10w30 mostly and then 5w30 with newer trucks. Seldom pushed a truck over 4 thousand miles between oil/filter changes back then, before synthetic oil. Had several friends here in town, that operated auto repair garages. Each had their own opinion on oil life and only one was into synthetics when they came on the scene and he was the least opinionated/bull headed one in the bunch.
Customer brought a full sized MOPAR in for engine replacement back in the mid 90s, think it had a 318 in it? Had already put one new Jasper replacement engine in it and was going for a warranty replacement. We pulled the oil pan. Sludge was so thick, garage buddy stuck an 18" screwdriver in the gook. JASPER dealer showed up, looked at the still vertical screwdriver and laughed.
Car owner claimed he'd had the oil changed every 3K. Um, nope. Warranty test failure.
