Way to bump a 7 year old dead thread answering the OP
I use Shell and avoid Chevron
I saw some research years ago about the various additive blends used by the various gas companies per region. Tried finding it just now with no luck. The data showed the additive package in Shell V-Power was clearly superior to others. Chevron's additives are good for longevity and not much else. Or course that was probably 5+ years ago. Who knows what has changed in that time.