I do mine at 15K like the manual states. I also drain my filter cannister about once a month to make sure no crap or water is building up.
BTW, that is what my filter usually looks like when I change it. I would be willing to bet it would look like that if i changed it a 500, 5000, or 15000 miles.
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2006 Dodge, 2500, CTD, 4x4, 6 Speed, SLT, Thunder Road Package, Mineral Grey, MBRP Muffler Replacement Kit, Fast Idle Enabled.