I have a 99 with about 26K in it, and my minder is telling me I'm at 100% too.
From past conversations I've read here on TDR, you may have a restricted filter but if your not doing some hard hauling and really producing the power and some WOT, you maynot get a sign from the minder that the filter is dirty (or dirty enough to make the sender register with a light foot on the go pedal).
I know I've done some heavy pulls up steep grades with WOT... so I thought I would have seen something on the minder... but nope.
I buy the geno's filter kit. I'm on my last oil and fuel filter. So I'm just gonna change the air filter anyway when I do the fuel filter next month. With the heat and temp transitions, I'm sure the foam layer and filter elements break down anyway. Cheap insurance and at the price of the genos filter kit (vs cummins or the stealer), it and a fuel filter are "free" anyway.
One last thought... . Also check all your breather hoses and turbo hoses to make sure they are good and tight so that no other source of fresh air is being drawn from. Again, I've read threads here on TDR of the post turbo hoses being loose.