AFE Stage II with the Proguard 7 filter. You won't see any big gains out of it, but you will hear the turbo a little better. I also have the pre-filter for it too. Although, you will be referred to spicer's air filter study so, I will post the link for you and make up your own decision : http://www.duramax-diesel.com/spicer/index.htm
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