So my Wife has a 2011 Silverado 5.3 with just over 20K on it and ever since I have changed oil since new inc. the break in oil the truck has always had lifter rattle on startup. Well we had some nice weather here last week so I thought I would change it for her. This time I used some Mobil 1 5W30 I have had in the garage for 2 years so I thought, WTH lets give it a shot. I will tell you the engine is so quiet now and has 0 lifter noise now, 1st time ever for this truck, so I was pretty happy about that. I am so impressed with it I may try some in my own car if it does not have oil leaks as I know the synthetics do leak more than conventional oil. Anyway Pretty happy with Mobil 1.